Showing papers by "Lawrence Berkeley National Laboratory published in 2013"
TL;DR: Metal-organic frameworks are porous materials that have potential for applications such as gas storage and separation, as well as catalysis, and methods are being developed for making nanocrystals and supercrystals of MOFs for their incorporation into devices.
Abstract: Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.
10,934 citations
TL;DR: The Materials Project (www.materialsproject.org) is a core program of the Materials Genome Initiative that uses high-throughput computing to uncover the properties of all known inorganic materials as discussed by the authors.
Abstract: Accelerating the discovery of advanced materials is essential for human welfare and sustainable, clean energy. In this paper, we introduce the Materials Project (www.materialsproject.org), a core program of the Materials Genome Initiative that uses high-throughput computing to uncover the properties of all known inorganic materials. This open dataset can be accessed through multiple channels for both interactive exploration and data mining. The Materials Project also seeks to create open-source platforms for developing robust, sophisticated materials analyses. Future efforts will enable users to perform ‘‘rapid-prototyping’’ of new materials in silico, and provide researchers with new avenues for cost-effective, data-driven materials design. © 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
6,566 citations
TL;DR: This RNA-guided DNA recognition platform provides a simple approach for selectively perturbing gene expression on a genome-wide scale and can efficiently repress expression of targeted genes in Escherichia coli, with no detectable off-target effects.
4,282 citations
TL;DR: The pymatgen library as mentioned in this paper is an open-source Python library for materials analysis that provides a well-tested set of structure and thermodynamic analyses relevant to many applications, and an open platform for researchers to collaboratively develop sophisticated analyses of materials data obtained both from first principles calculations and experiments.
2,364 citations
National Center for Atmospheric Research1, Pacific Northwest National Laboratory2, University of Toronto3, Los Alamos National Laboratory4, Cornell University5, University of Wisconsin-Madison6, Lawrence Livermore National Laboratory7, Lawrence Berkeley National Laboratory8, Oak Ridge National Laboratory9, University of Calgary10
TL;DR: The Community Earth System Model (CESM) as discussed by the authors is a community tool used to investigate a diverse set of Earth system interactions across multiple time and space scales, including biogeochemical cycles, a variety of atmospheric chemistry options, the Greenland Ice Sheet, and an atmosphere that extends to the lower thermosphere.
Abstract: The Community Earth System Model (CESM) is a flexible and extensible community tool used to investigate a diverse set of Earth system interactions across multiple time and space scales. This global coupled model significantly extends its predecessor, the Community Climate System Model, by incorporating new Earth system simulation capabilities. These comprise the ability to simulate biogeochemical cycles, including those of carbon and nitrogen, a variety of atmospheric chemistry options, the Greenland Ice Sheet, and an atmosphere that extends to the lower thermosphere. These and other new model capabilities are enabling investigations into a wide range of pressing scientific questions, providing new foresight into possible future climates and increasing our collective knowledge about the behavior and interactions of the Earth system. Simulations with numerous configurations of the CESM have been provided to phase 5 of the Coupled Model Intercomparison Project (CMIP5) and are being analyzed by the broad com...
2,075 citations
TL;DR: Observations suggest that the OER is catalyzed by Ni in Ni-Fe films and that the presence of Fe alters the redox properties of Ni, causing a positive shift in the potential at which Ni(OH)2/NiOOH redox occurs.
Abstract: A detailed investigation has been carried out of the structure and electrochemical activity of electrodeposited Ni-Fe films for the oxygen evolution reaction (OER) in alkaline electrolytes. Ni-Fe films with a bulk and surface composition of 40% Fe exhibit OER activities that are roughly 2 orders of magnitude higher than that of a freshly deposited Ni film and about 3 orders of magnitude higher than that of an Fe film. The freshly deposited Ni film increases in activity by as much as 20-fold during exposure to the electrolyte (KOH); however, all films containing Fe are stable as deposited. The oxidation of Ni(OH)2 to NiOOH in Ni films occurs at potentials below the onset of the OER. Incorporation of Fe into the film increases the potential at which Ni(OH)2/NiOOH redox occurs and decreases the average oxidation state of Ni in NiOOH. The Tafel slope (40 mV dec(-1)) and reaction order in OH(-) (1) for the mixed Ni-Fe films (containing up to 95% Fe) are the same as those for aged Ni films. In situ Raman spectra acquired in 0.1 M KOH at OER potentials show two bands characteristic of NiOOH. The relative intensities of these bands vary with Fe content, indicating a change in the local environment of Ni-O. Similar changes in the relative intensities of the bands and an increase in OER activity are observed when pure Ni films are aged. These observations suggest that the OER is catalyzed by Ni in Ni-Fe films and that the presence of Fe alters the redox properties of Ni, causing a positive shift in the potential at which Ni(OH)2/NiOOH redox occurs, a decrease in the average oxidation state of the Ni sites, and a concurrent increase in the activity of Ni cations for the OER.
1,951 citations
Kyle S. Dawson1, David J. Schlegel2, Christopher P. Ahn1, Scott F. Anderson3 +181 more•Institutions (51)
TL;DR: The Baryon Oscillation Spectroscopic Survey (BOSS) as discussed by the authors was designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure.
Abstract: The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the scale of baryon acoustic oscillations (BAO) in the clustering of matter over a larger volume than the combined efforts of all previous spectroscopic surveys of large-scale structure. BOSS uses 1.5 million luminous galaxies as faint as i = 19.9 over 10,000 deg2 to measure BAO to redshifts z < 0.7. Observations of neutral hydrogen in the Lyα forest in more than 150,000 quasar spectra (g < 22) will constrain BAO over the redshift range 2.15 < z < 3.5. Early results from BOSS include the first detection of the large-scale three-dimensional clustering of the Lyα forest and a strong detection from the Data Release 9 data set of the BAO in the clustering of massive galaxies at an effective redshift z = 0.57. We project that BOSS will yield measurements of the angular diameter distance dA to an accuracy of 1.0% at redshifts z = 0.3 and z = 0.57 and measurements of H(z) to 1.8% and 1.7% at the same redshifts. Forecasts for Lyα forest constraints predict a measurement of an overall dilation factor that scales the highly degenerate DA (z) and H –1(z) parameters to an accuracy of 1.9% at z ~ 2.5 when the survey is complete. Here, we provide an overview of the selection of spectroscopic targets, planning of observations, and analysis of data and data quality of BOSS.
1,938 citations
University of Exeter1, ETH Zurich2, Bureau of Meteorology3, Université catholique de Louvain4, China Meteorological Administration5, Iowa State University6, Met Office7, Joseph Fourier University8, South African Weather Service9, Climate Central10, University of Victoria11, Lawrence Berkeley National Laboratory12
TL;DR: The authors assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system.
Abstract: This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986–2005, unless otherwise stated.
1,719 citations
TL;DR: A new class of Pt-Co nanocatalysts composed of ordered Pt(3)Co intermetallic cores with a 2-3 atomic-layer-thick platinum shell with high activity and stability are described, providing a new direction for catalyst performance optimization for next-generation fuel cells.
Abstract: To enhance and optimize nanocatalyst performance and durability for the oxygen reduction reaction in fuel-cell applications, we look beyond Pt-metal disordered alloys and describe a new class of Pt-Co nanocatalysts composed of ordered Pt(3)Co intermetallic cores with a 2-3 atomic-layer-thick platinum shell. These nanocatalysts exhibited over 200% increase in mass activity and over 300% increase in specific activity when compared with the disordered Pt(3)Co alloy nanoparticles as well as Pt/C. So far, this mass activity for the oxygen reduction reaction is the highest among the Pt-Co systems reported in the literature under similar testing conditions. Stability tests showed a minimal loss of activity after 5,000 potential cycles and the ordered core-shell structure was maintained virtually intact, as established by atomic-scale elemental mapping. The high activity and stability are attributed to the Pt-rich shell and the stable intermetallic Pt(3)Co core arrangement. These ordered nanoparticles provide a new direction for catalyst performance optimization for next-generation fuel cells.
1,689 citations
University of Adelaide1, University of Wisconsin-Madison2, Ghent University3, University of Canterbury4, University of Geneva5, Humboldt University of Berlin6, University of California, Irvine7, University of Mainz8, University of California, Berkeley9, Ohio State University10, Université libre de Bruxelles11, Ruhr University Bochum12, University of Wuppertal13, University of Maryland, College Park14, University of Kansas15, Lawrence Berkeley National Laboratory16, RWTH Aachen University17, Uppsala University18, University of Alberta19, Stockholm University20, Vrije Universiteit Brussel21, University of Bonn22, École Polytechnique Fédérale de Lausanne23, Georgia Institute of Technology24, Pennsylvania State University25, Technical University of Dortmund26, Southern University and A&M College27
TL;DR: The presence of a high-energy neutrino flux containing the most energetic neutrinos ever observed is revealed, including 28 events at energies between 30 and 1200 TeV, although the origin of this flux is unknown and the findings are consistent with expectations for a neutRino population with origins outside the solar system.
Abstract: We report on results of an all-sky search for high-energy neutrino events interacting within the IceCube neutrino detector conducted between May 2010 and May 2012. The search follows up on the previous detection of two PeV neutrino events, with improved sensitivity and extended energy coverage down to about 30 TeV. Twenty-six additional events were observed, substantially more than expected from atmospheric backgrounds. Combined, both searches reject a purely atmospheric origin for the 28 events at the 4 sigma level. These 28 events, which include the highest energy neutrinos ever observed, have flavors, directions, and energies inconsistent with those expected from the atmospheric muon and neutrino backgrounds. These properties are, however, consistent with generic predictions for an additional component of extraterrestrial origin.
1,490 citations
TL;DR: In vitro selection and high-throughput sequencing results show that guide-RNA:Cas9 specificity extends past a 7- to 12-base-pair seed sequence, and suggest a tradeoff between activity and specificity both in vitro and in cells as a shorter, less-active guide RNA is more specific than a longer, more- active guide RNA.
Abstract: The RNA-programmable Cas9 endonuclease cleaves double-stranded DNA at sites complementary to a 20-base-pair guide RNA. The Cas9 system has been used to modify genomes in multiple cells and organisms, demonstrating its potential as a facile genome-engineering tool. We used in vitro selection and high-throughput sequencing to determine the propensity of eight guide-RNA:Cas9 complexes to cleave each of 10(12) potential off-target DNA sequences. The selection results predicted five off-target sites in the human genome that were confirmed to undergo genome cleavage in HEK293T cells upon expression of one of two guide-RNA:Cas9 complexes. In contrast to previous models, our results show that guide-RNA:Cas9 specificity extends past a 7- to 12-base-pair seed sequence. Our results also suggest a tradeoff between activity and specificity both in vitro and in cells as a shorter, less-active guide RNA is more specific than a longer, more-active guide RNA. High concentrations of guide-RNA:Cas9 complexes can cleave off-target sites containing mutations near or within the PAM that are not cleaved when enzyme concentrations are limiting.
TL;DR: In this paper, the band offsets and heterostructures of monolayer and few-layer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) are investigated from first principles calculations.
Abstract: The band offsets and heterostructures of monolayer and few-layer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) are investigated from first principles calculations. The band alignments between different MX2 monolayers are calculated using the vacuum level as reference, and a simple model is proposed to explain the observed chemical trends. Some of the monolayers and their heterostructures show band alignments suitable for potential applications in spontaneous water splitting, photovoltaics, and optoelectronics. The strong dependence of the band offset on the number of layers also implicates a possible way of patterning quantum structures with thickness engineering.
TL;DR: In this article, the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings were extracted from data with full 2-loop NNLO precision.
Abstract: We extract from data the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings with full 2-loop NNLO precision, and we extrapolate the SM parameters up to large energies with full 3-loop NNLO RGE precision. Then we study the phase diagram of the Standard Model in terms of high-energy parameters, finding that the measured Higgs mass roughly corresponds to the minimum values of the Higgs quartic and top Yukawa and the maximum value of the gauge couplings allowed by vacuum metastability. We discuss various theoretical interpretations of the near-criticality of the Higgs mass.
TL;DR: This work reports the first user-interactive e-skin that not only spatially maps the applied pressure but also provides an instantaneous visual response through a built-in active-matrix organic light-emitting diode display with red, green and blue pixels.
Abstract: Electr onic skin (e-skin) presents a network of mechanically flexible sensors that can conformally wrap irregular surfaces and spatially map and quantify various stimuli 1‐12 . Previous works on e-skin have focused on the optimization of pressure sensors interfaced with an electronic readout, whereas user interfaces based on a human-readable output were not explored. Here, we report the first user-interactive e-skin that not only spatially maps the applied pressure but also provides an instantaneous visual response through a built-in active-matrix organic light-emitting diode display with red, green and blue pixels. In this system, organic light-emitting diodes (OLEDs) are turned on locally where the surface is touched, and the intensity of the emitted light quantifies the magnitude of the applied pressure. This work represents a system-on-plastic 4,13‐17 demonstration where three distinct electronic components— thin-film transistor, pressure sensor and OLED arrays—are monolithically integrated over large areas on a single plastic substrate. The reported e-skin may find a wide range of applications in interactive input/control devices, smart wallpapers, robotics and medical/health monitoring devices.
TL;DR: A strong photonic SHE resulting in a measured large splitting of polarized light at metasurfaces is reported, which may provide a route for exploiting the spin and orbit angular momentum of light for information processing and communication.
Abstract: The spin Hall effect (SHE) of light is very weak because of the extremely small photon momentum and spin-orbit interaction. Here, we report a strong photonic SHE resulting in a measured large splitting of polarized light at metasurfaces. The rapidly varying phase discontinuities along a metasurface, breaking the axial symmetry of the system, enable the direct observation of large transverse motion of circularly polarized light, even at normal incidence. The strong spin-orbit interaction deviates the polarized light from the trajectory prescribed by the ordinary Fermat principle. Such a strong and broadband photonic SHE may provide a route for exploiting the spin and orbit angular momentum of light for information processing and communication.
TL;DR: The results of theoretical investigations of the relative stability of layered and spinel bulk phases of Co oxides, as well as the stability of selected surfaces as a function of applied potential and pH are reported.
Abstract: The presence of layered cobalt oxides has been identified experimentally in Co-based anodes under oxygen-evolving conditions. In this work, we report the results of theoretical investigations of the relative stability of layered and spinel bulk phases of Co oxides, as well as the stability of selected surfaces as a function of applied potential and pH. We then study the oxygen evolution reaction (OER) on these surfaces and obtain activity trends at experimentally relevant electro-chemical conditions. Our calculated volume Pourbaix diagram shows that β-CoOOH is the active phase where the OER occurs in alkaline media. We calculate relative surface stabilities and adsorbate coverages of the most stable low-index surfaces of β-CoOOH: (0001), (0112), and (1014). We find that at low applied potentials, the (1014) surface is the most stable, while the (0112) surface is the more stable at higher potentials. Next, we compare the theoretical overpotentials for all three surfaces and find that the (1014) surface is the most active one as characterized by an overpotential of η = 0.48 V. The high activity of the (1014) surface can be attributed to the observation that the resting state of Co in the active site is Co(3+) during the OER, whereas Co is in the Co(4+) state in the less active surfaces. Lastly, we demonstrate that the overpotential of the (1014) surface can be lowered further by surface substitution of Co by Ni. This finding could explain the experimentally observed enhancement in the OER activity of Ni(y)Co(1-y)O(x) thin films with increasing Ni content. All energetics in this work were obtained from density functional theory using the Hubbard-U correction.
Johns Hopkins University1, Princeton University2, Carnegie Institution for Science3, Lawrence Berkeley National Laboratory4, University of California, Santa Cruz5, University of Washington6, University of Utah7, Apache Corporation8, Ohio State University9, Case Western Reserve University10, Fermilab11, University of Pennsylvania12, Massachusetts Institute of Technology13, Spanish National Research Council14, Space Telescope Science Institute15, University of Sussex16, California Institute of Technology17, New York University18, Argonne National Laboratory19, Pennsylvania State University20, University of Wisconsin-Madison21, Ames Research Center22, University of Chicago23
TL;DR: In this article, the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS) were presented.
Abstract: We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5 m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyα absorption of 160,000 high redshift quasars over 10,000 deg2 of sky, making percent level measurements of the absolute cosmic distance scale of the universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near-ultraviolet to the near-infrared, with a resolving power R = λ/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 nm < λ < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.
TL;DR: This work investigates effects of anion vacancies in monolayer transition metal dichalcogenides as two-dimensional (2D) semiconductors where the vacancies density is controlled by α-particle irradiation or thermal-annealing and finds a new, sub-bandgap emission peak as well as increase in overall photoluminescence intensity as a result of the vacancy generation.
Abstract: Point defects in semiconductors can trap free charge carriers and localize excitons. The interaction between these defects and charge carriers becomes stronger at reduced dimensionalities, and is expected to greatly influence physical properties of the hosting material. We investigated effects of anion vacancies in monolayer transition metal dichalcogenides as two-dimensional (2D) semiconductors where the vacancies density is controlled bya-particle irradiation or thermal-annealing. We found a new, sub-bandgap emission peak as well as increase in overall photoluminescence intensity as a result of the vacancy generation. Interestingly, these effects are absent when measured in vacuum. We conclude that in opposite to conventional wisdom, optical quality at room temperature cannot be used as criteria to assess crystal quality of the 2D semiconductors. Our results not only shed light on defect and exciton physics of 2D semiconductors, but also offer a new route toward tailoring optical properties of 2D semiconductors by defect engineering.
TL;DR: In this article, the authors evaluated 20-year temperature and precipitation extremes and their projected future changes in an ensemble of climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), updating a similar study based on the CMIP3 ensemble.
Abstract: Twenty-year temperature and precipitation extremes and their projected future changes are evaluated in an ensemble of climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), updating a similar study based on the CMIP3 ensemble. The projected changes are documented for three radiative forcing scenarios. The performance of the CMIP5 models in simulating 20-year temperature and precipitation extremes is comparable to that of the CMIP3 ensemble. The models simulate late 20th century warm extremes reasonably well, compared to estimates from reanalyses. The model discrepancies in simulating cold extremes are generally larger than those for warm extremes. Simulated late 20th century precipitation extremes are plausible in the extratropics but uncertainty in extreme precipitation in the tropics and subtropics remains very large, both in the models and the observationally-constrained datasets. Consistent with CMIP3 results, CMIP5 cold extremes generally warm faster than warm extremes, mainly in regions where snow and sea-ice retreat with global warming. There are tropical and subtropical regions where warming rates of warm extremes exceed those of cold extremes. Relative changes in the intensity of precipitation extremes generally exceed relative changes in annual mean precipitation. The corresponding waiting times for late 20th century extreme precipitation events are reduced almost everywhere, except for a few subtropical regions. The CMIP5 planetary sensitivity in extreme precipitation is about 6 %/°C, with generally lower values over extratropical land.
TL;DR: It is revealed that stable microvasculature constitutes a dormant niche, whereas sprouting neovasculature sparks micrometastatic outgrowth, which is a surprising result in dormancy models and in zebrafish.
Abstract: In a significant fraction of breast cancer patients, distant metastases emerge after years or even decades of latency. How disseminated tumour cells (DTCs) are kept dormant, and what wakes them up, are fundamental problems in tumour biology. To address these questions, we used metastasis assays in mice and showed that dormant DTCs reside on microvasculature of lung, bone marrow and brain. We then engineered organotypic microvascular niches to determine whether endothelial cells directly influence breast cancer cell (BCC) growth. These models demonstrated that endothelial-derived thrombospondin-1 induces sustained BCC quiescence. This suppressive cue was lost in sprouting neovasculature; time-lapse analysis showed that sprouting vessels not only permit, but accelerate BCC outgrowth. We confirmed this surprising result in dormancy models and in zebrafish, and identified active TGF-β1 and periostin as tumour-promoting factors derived from endothelial tip cells. Our work reveals that stable microvasculature constitutes a dormant niche, whereas sprouting neovasculature sparks micrometastatic outgrowth.
TL;DR: Uremia profoundly alters the composition of the gut microbiome and the biological impact of this phenomenon is unknown and awaits further investigation.
TL;DR: These two neutrino-induced events could be a first indication of an astrophysical neutrinos flux; the moderate significance, however, does not permit a definitive conclusion at this time.
Abstract: We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of 1.04 +/- 0.16 and 1.14 +/- 0.17 PeV, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current nu(e,mu,tau) ((nu) over bar (e,mu,tau)) or charged-current nu(e) ((nu) over bar (e)) interactions within the IceCube detector. The events were discovered in a search for ultrahigh energy neutrinos using data corresponding to 615.9 days effective live time. The expected number of atmospheric background is 0.082 +/- 0.004(stat)(-0.057)(+0.041)(syst). The probability of observing two or more candidate events under the atmospheric background-only hypothesis is 2.9 x 10(-3) (2.8 sigma) taking into account the uncertainty on the expected number of background events. These two events could be a first indication of an astrophysical neutrino flux; the moderate significance, however, does not permit a definitive conclusion at this time.
University of Pittsburgh1, University of California, Irvine2, University of California, Berkeley3, University of California, Santa Cruz4, University of California, San Diego5, Alfred P. Sloan Foundation6, Harvard University7, Max Planck Society8, Lawrence Berkeley National Laboratory9, University of Arizona10, University of Kentucky11, Goddard Space Flight Center12, California Institute of Technology13, Space Telescope Science Institute14, University of Southern California15, University of Washington16, Academia Sinica17, Sonoma State University18, Liverpool John Moores University19
TL;DR: The DEEP2 Galaxy Redshift Survey (DEEP2) as discussed by the authors is the largest high-precision redshift survey of galaxies at z ~ 1 completed to date, covering an area of 2.8 deg^2 divided into four separate fields observed to a limiting apparent magnitude of R_(AB) = 24.1.
Abstract: We describe the design and data analysis of the DEEP2 Galaxy Redshift Survey, the densest and largest high-precision redshift survey of galaxies at z ~ 1 completed to date. The survey was designed to conduct a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude M_B = −20 at z ~ 1 via ~90 nights of observation on the Keck telescope. The survey covers an area of 2.8 deg^2 divided into four separate fields observed to a limiting apparent magnitude of R_(AB) = 24.1. Objects with z ≾0.7 are readily identifiable using BRI photometry and rejected in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5 times more efficiently than in a purely magnitude-limited sample. Approximately 60% of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets that fail to yield secure redshifts are blue objects that lie beyond z ~ 1.45, where the [O ii] 3727 A doublet lies in the infrared. The DEIMOS 1200 line mm^(−1) grating used for the survey delivers high spectral resolution (R ~ 6000), accurate and secure redshifts, and unique internal kinematic information. Extensive ancillary data are available in the DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into one of the richest multiwavelength regions on the sky. This paper is intended as a handbook for users of the DEEP2 Data Release 4, which includes all DEEP2 spectra and redshifts, as well as for the DEEP2 DEIMOS data reduction pipelines. Extensive details are provided on object selection, mask design, biases in target selection and redshift measurements, the spec2d two-dimensional data-reduction pipeline, the spec1d automated redshift pipeline, and the zspec visual redshift verification process, along with examples of instrumental signatures or other artifacts that in some cases remain after data reduction. Redshift errors and catastrophic failure rates are assessed through more than 2000 objects with duplicate observations. Sky subtraction is essentially photon-limited even under bright OH sky lines; we describe the strategies that permitted this, based on high image stability, accurate wavelength solutions, and powerful B-spline modeling methods. We also investigate the impact of targets that appear to be single objects in ground-based targeting imaging but prove to be composite in Hubble Space Telescope data; they constitute several percent of targets at z ~ 1, approaching ~5%–10% at z > 1.5. Summary data are given that demonstrate the superiority of DEEP2 over other deep high-precision redshift surveys at z ~ 1 in terms of redshift accuracy, sample number density, and amount of spectral information. We also provide an overview of the scientific highlights of the DEEP2 survey thus far.
TL;DR: This work introduces tin-doped indium oxide nanocrystals into niobium oxide glass (NbOx), and realizes a new amorphous structure as a consequence of linking it to the nanocry crystals, which demonstrates a previously unrealized optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows.
Abstract: Amorphous metal oxides are useful in optical, electronic and electrochemical devices. The bonding arrangement within these glasses largely determines their properties, yet it remains a challenge to manipulate their structures in a controlled manner. Recently, we developed synthetic protocols for incorporating nanocrystals that are covalently bonded into amorphous materials. This 'nanocrystal-in-glass' approach not only combines two functional components in one material, but also the covalent link enables us to manipulate the glass structure to change its properties. Here we illustrate the power of this approach by introducing tin-doped indium oxide nanocrystals into niobium oxide glass (NbOx), and realize a new amorphous structure as a consequence of linking it to the nanocrystals. The resulting material demonstrates a previously unrealized optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows. These transparent films can block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts. We also show that the reconstructed NbOx glass has superior properties-its optical contrast is enhanced fivefold and it has excellent electrochemical stability, with 96 per cent of charge capacity retained after 2,000 cycles.
TL;DR: An expression cassette architecture for genetic elements controlling transcription and translation initiation in Escherichia coli is developed, demonstrating that arbitrary genes are reliably expressed to within twofold relative target expression windows with ∼93% reliability.
Abstract: An inability to reliably predict quantitative behaviors for novel combinations of genetic elements limits the rational engineering of biological systems. We developed an expression cassette architecture for genetic elements controlling transcription and translation initiation in Escherichia coli: transcription elements encode a common mRNA start, and translation elements use an overlapping genetic motif found in many natural systems. We engineered libraries of constitutive and repressor-regulated promoters along with translation initiation elements following these definitions. We measured activity distributions for each library and selected elements that collectively resulted in expression across a 1,000-fold observed dynamic range. We studied all combinations of curated elements, demonstrating that arbitrary genes are reliably expressed to within twofold relative target expression windows with ∼93% reliability. We expect the genetic element definitions validated here can be collectively expanded to create collections of public-domain standard biological parts that support reliable forward engineering of gene expression at genome scales.
TL;DR: An improvement of more than two orders of magnitude is demonstrated in the spin coherence time of nitrogen-vacancy centres of diamond, which could advance quantum sensing, enable squeezing and many-body entanglement, and open a path to simulating driven, interaction-dominated quantum many- body Hamiltonians.
Abstract: Nitrogen-vacancy centres in diamond are a promising route for solid-state quantum information processing and magnetometry, but longer coherence times are needed to optimize protocols. Here, Bar-Gill et al. suppress decoherence to realize nitrogen-vacancy spin coherence times approaching one second.
TL;DR: The results here demonstrate the need of degenerate doping of few-layer chalcogenides to improve the contact resistances and further realize high performance and complementary channel electronics.
Abstract: We report here the first degenerate n-doping of few-layer MoS2 and WSe2 semiconductors by surface charge transfer using potassium. High-electron sheet densities of ~1.0 × 10(13) cm(-2) and 2.5 × 10(12) cm(-2) for MoS2 and WSe2 are obtained, respectively. In addition, top-gated WSe2 and MoS2 n-FETs with selective K doping at the metal source/drain contacts are fabricated and shown to exhibit low contact resistances. Uniquely, WSe2 n-FETs are reported for the first time, exhibiting an electron mobility of ~110 cm(2)/V·s, which is comparable to the hole mobility of previously reported p-FETs using the same material. Ab initio simulations were performed to understand K doping of MoS2 and WSe2 in comparison with graphene. The results here demonstrate the need of degenerate doping of few-layer chalcogenides to improve the contact resistances and further realize high performance and complementary channel electronics.
TL;DR: Physi-sorbed O2 and/or H2O molecules electronically deplete n-type materials such as MoS2 and MoSe2, which weakens electrostatic screening that would otherwise destabilize excitons, leading to the drastic enhancement in photoluminescence.
Abstract: In the monolayer limit, transition metal dichalcogenides become direct-bandgap, light-emitting semiconductors. The quantum yield of light emission is low and extremely sensitive to the substrate used, while the underlying physics remains elusive. In this work, we report over 100 times modulation of light emission efficiency of these two-dimensional semiconductors by physical adsorption of O2 and/or H2O molecules, while inert gases do not cause such effect. The O2 and/or H2O pressure acts quantitatively as an instantaneously reversible “molecular gating” force, providing orders of magnitude broader control of carrier density and light emission than conventional electric field gating. Physi-sorbed O2 and/or H2O molecules electronically deplete n-type materials such as MoS2 and MoSe2, which weakens electrostatic screening that would otherwise destabilize excitons, leading to the drastic enhancement in photoluminescence. In p-type materials such as WSe2, the molecular physisorption results in the opposite eff...
TL;DR: In this paper, a review of the experimental techniques used for characterizing spinor gases, their mean-field and many-body ground states, both in isolation and under the application of symmetry-breaking external fields, are discussed.
Abstract: Spinor Bose gases form a family of quantum fluids manifesting both magnetic order and superfluidity. This article reviews experimental and theoretical progress in understanding the static and dynamic properties of these fluids. The connection between system properties and the rotational symmetry properties of the atomic states and their interactions are investigated. Following a review of the experimental techniques used for characterizing spinor gases, their mean-field and many-body ground states, both in isolation and under the application of symmetry-breaking external fields, are discussed. These states serve as the starting point for understanding low-energy dynamics, spin textures and topological defects, effects of magnetic dipole interactions, and various non-equilibrium collective spin-mixing phenomena. The paper aims to form connections and establish coherence among the vast range of works on spinor Bose gases, so as to point to open questions and future research opportunities.
TL;DR: The volume of correlation, Vc, is defined, a SAS invariant derived from the scattered intensities that is specific to the structural state of the particle, but independent of concentration and the requirements of a compact, folded particle.
Abstract: Modern small-angle scattering (SAS) experiments with X-rays or neutrons provide a comprehensive, resolution-limited observation of the thermodynamic state. However, methods for evaluating mass and validating SAS-based models and resolution have been inadequate. Here we define the volume of correlation, Vc, a SAS invariant derived from the scattered intensities that is specific to the structural state of the particle, but independent of concentration and the requirements of a compact, folded particle. We show that Vc defines a ratio, QR, that determines the molecular mass of proteins or RNA ranging from 10 to 1,000 kilodaltons. Furthermore, we propose a statistically robust method for assessing model-data agreements (χ(2)free) akin to cross-validation. Our approach prevents over-fitting of the SAS data and can be used with a newly defined metric, RSAS, for quantitative evaluation of resolution. Together, these metrics (Vc, QR, χ(2)free and RSAS) provide analytical tools for unbiased and accurate macromolecular structural characterizations in solution.