Showing papers by "Rensselaer Polytechnic Institute published in 2006"

Corporate Social Responsibility: Strategic Implications*

Abstract: We describe a variety of perspectives on corporate social responsibility (CSR), which we use to develop a framework for consideration of the strategic implications of CSR. Based on this framework, we propose an agenda for additional theoretical and empirical research on CSR. We then review the papers in this special issue and relate them to the proposed agenda.

Crystallization thermometers for zircon and rutile

Abstract: Zircon and rutile are common accessory minerals whose essential structural constituents, Zr, Ti, and Si can replace one another to a limited extent. Here we present the combined results of high pressure–temperature experiments and analyses of natural zircons and rutile crystals that reveal systematic changes with temperature in the uptake of Ti in zircon and Zr in rutile. Detailed calibrations of the temperature dependencies are presented as two geothermometers—Ti content of zircon and Zr content of rutile—that may find wide application in crustal petrology. Synthetic zircons were crystallized in the presence of rutile at 1–2 GPa and 1,025–1,450°C from both silicate melts and hydrothermal solutions, and the resulting crystals were analyzed for Ti by electron microprobe (EMP). To augment and extend the experimental results, zircons hosted by five natural rocks of well-constrained but diverse origin (0.7–3 GPa; 580–1,070°C) were analyzed for Ti, in most cases by ion microprobe (IMP). The combined experimental and natural results define a log-linear dependence of equilibrium Ti content (expressed in ppm by weight) upon reciprocal temperature: $$\log ({\text{Ti}}_{{{\text{zircon}}}}) = (6.01 \pm 0.03) - \frac{{5080 \pm 30}}{{T\;(\hbox{K})}}.$$ In a strategy similar to that used for zircon, rutile crystals were grown in the presence of zircon and quartz (or hydrous silicic melt) at 1–1.4 GPa and 675–1,450°C and analyzed for Zr by EMP. The experimental results were complemented by EMP analyses of rutile grains from six natural rocks of diverse origin spanning 0.35–3 GPa and 470–1,070°C. The concentration of Zr (ppm by weight) in the synthetic and natural rutiles also varies in log-linear fashion with T −1: $$\log ({\text{Zr}}_{{{\text{rutile}}}}) = (7.36 \pm 0.10) - \frac{{4470 \pm 120}}{{T\;(\hbox{K})}}.$$ The zircon and rutile calibrations are consistent with one another across both the synthetic and natural samples, and are relatively insensitive to changes in pressure, particularly in the case of Ti in zircon. Applied to natural zircons and rutiles of unknown provenance and/or growth conditions, the thermometers have the potential to return temperatures with an estimated uncertainty of ±10 ° or better in the case of zircon and ±20° or better in the case of rutile over most of the temperature range of interest (∼400–1,000°C). Estimates of relative temperature or changes in temperature (e.g., from zoning profiles in a single mineral grain) made with these thermometers are subject to analytical uncertainty only, which can be better than ±5° depending on Ti or Zr concentration (i.e., temperature), and also upon the analytical instrument (e.g., IMP or EMP) and operating conditions.

Light-Emitting Diodes by E. Fred Schubert

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Opportunity Recognition as the Detection of Meaningful Patterns: Evidence from Comparisons of Novice and Experienced Entrepreneurs

Abstract: It is suggested that the recognition of new business opportunities often involves pattern recognition---the cognitive process through which individuals identify meaningful patterns in complex arrays of events or trends. Basic research on pattern recognition indicates that cognitive frameworks acquired through experience (e.g., prototypes) play a central role in this process. Such frameworks provide individuals with a basis for noticing connections between seemingly independent events or trends (e.g., advances in technology, shifts in markets, changes in government policies, etc.), and for detecting meaningful patterns in these connections. We propose that ideas for new products or services often emerge from the perception of such patterns. New business opportunities are identified when entrepreneurs, using relevant cognitive frameworks, “connect the dots” between seemingly unrelated events or trends and then detect patterns in these connections suggestive of new products or services. To obtain evidence on these proposals, we compared the “business opportunity” prototypes of novice (first-time) and repeat (experienced) entrepreneurs---their cognitive representations of the essential nature of opportunities. As predicted, the prototypes of experienced entrepreneurs were more clearly defined, richer in content, and more concerned with factors and conditions related to actually starting and running a new venture (e.g., generation of positive cash flow) than the prototypes of novice entrepreneurs. These findings offer support for the view that pattern recognition is a key component of opportunity recognition.

Opportunity Recognition as Pattern Recognition: How Entrepreneurs “Connect the Dots” to Identify New Business Opportunities

Abstract: Executive Overview How do entrepreneurs identify opportunities for new business ventures? One possibility, suggested by research on human cognition, is that they do so by using cognitive frameworks they have acquired through experience to perceive connections between seemingly unrelated events or trends in the external world. In other words, they use cognitive frameworks they possess to “connect the dots” between changes in technology, demographics, markets, government policies, and other factors. The patterns they then perceive in these events or trends suggest ideas for new products or services—ideas that can potentially serve as the basis for new ventures. This pattern recognition perspective on opportunity identification is useful in several respects. First, it helps integrate into one basic framework three factors that have been found to play an important role in opportunity recognition: engaging in an active search for opportunities; alertness to them; and prior knowledge of an industry or market. I...

The fourth data release of the Sloan Digital Sky Survey

Abstract: This paper describes the Fourth Data Release of the Sloan Digital Sky Survey (SDSS), including all survey-quality data taken through 2004 June. The data release includes five-band photometric data for 180 million objects selected over 6670 deg2 and 673,280 spectra of galaxies, quasars, and stars selected from 4783 deg2 of those imaging data using the standard SDSS target selection algorithms. These numbers represent a roughly 27% increment over those of the Third Data Release; all the data from previous data releases are included in the present release. The Fourth Data Release also includes an additional 131,840 spectra of objects selected using a variety of alternative algorithms, to address scientific issues ranging from the kinematics of stars in the Milky Way thick disk to populations of faint galaxies and quasars.

The Field of Streams: Sagittarius and its Siblings

Abstract: We use Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) u, g, r, i, z photometry to study Milky Way halo substructure in the area around the north Galactic cap. A simple color cut (g - r < 0.4) reveals the tidal stream of the Sagittarius dwarf spheroidal galaxy, as well as a number of other stellar structures in the field. Two branches (A and B) of the Sagittarius stream are clearly visible in an RGB composite image created from three magnitude slices, and there is also evidence for a still more distant wrap behind the A branch. A comparison of these data with numerical models suggests that the shape of the Galactic dark halo is close to spherical.

Link prediction using supervised learning

Abstract: Social network analysis has attracted much attention in recent years. Link prediction is a key research directions within this area. In this research, we study link prediction as a supervised learning task. Along the way, we identify a set of features that are key to the superior performance under the supervised learning setup. The identified features are very easy to compute, and at the same time surprisingly effective in solving the link prediction problem. We also explain the effectiveness of the features from their class density distribution. Then we compare different classes of supervised learning algorithms in terms of their prediction performance using various performance metrics, such as accuracy, precision-recall, F-values, squared error etc. with a 5-fold cross validation. Our results on two practical social network datasets shows that most of the well-known classification algorithms (decision tree, k-nn,multilayer perceptron, SVM, rbf network) can predict link with surpassing performances, but SVM defeats all of them with narrow margin in all different performance measures. Again, ranking of features with popular feature ranking algorithms shows that a small subset of features always plays a significant role in the link prediction job.

The Field of Streams: Sagittarius and its Siblings

Abstract: We use Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) u,g,r,i,z photometry to study Milky Way halo substructure in the area around the North Galactic Cap. A simple color cut (g-r < 0.4) reveals the tidal stream of the Sagittarius dwarf spheroidal, as well as a number of other stellar structures in the field. Two branches (A and B) of the Sagittarius stream are clearly visible in an RGB-composite image created from 3 magnitude slices, and there is also evidence for a still more distant wrap behind the A branch. A comparison of these data with numerical models suggests that the shape of the Galactic dark halo is close to spherical.

Multifunctional composites using reinforced laminae with carbon-nanotube forests

Abstract: Traditional fibre-reinforced composite materials with excellent in-plane properties fare poorly when out-of-plane through-thickness properties are important1. Composite architectures with fibres designed orthogonal to the two-dimensional (2D) layout in traditional composites could alleviate this weakness in the transverse direction, but all of the efforts1,2 so far have only produced limited success. Here, we unveil an approach to the 3D composite challenge, without altering the 2D stack design, on the basis of the concept of interlaminar carbon-nanotube3,4 forests that would provide enhanced multifunctional properties along the thickness direction. The carbon-nanotube forests allow the fastening of adjacent plies in the 3D composite. We grow multiwalled carbon nanotubes on the surface of micro-fibre fabric cloth layouts, normal to the fibre lengths, resulting in a 3D effect between plies under loading. These nanotube-coated fabric cloths serve as building blocks for the multilayered 3D composites, with the nanotube forests providing much-needed interlaminar strength and toughness under various loading conditions. For the fabricated 3D composites with nanotube forests, we demonstrate remarkable improvements in the interlaminar fracture toughness, hardness, delamination resistance, in-plane mechanical properties, damping, thermoelastic behaviour, and thermal and electrical conductivities making these structures truly multifunctional.

Experimental investigation of temperature and volume fraction variations on the effective thermal conductivity of nanoparticle suspensions (nanofluids)

Abstract: An experimental investigation was conducted to examine the effects of variations in the temperature and volume fraction on the steady-state effective thermal conductivity of two different nanoparticle suspensions. Copper and aluminum oxide, CuO and Al2O3, nanoparticles with area weighted diameters of 29 and 36nm, respectively, were blended with distilled water at 2%, 4%, 6%, and 10% volume fractions and the resulting suspensions were evaluated at temperatures ranging from 27.5to34.7°C. The results indicate that the nanoparticle material, diameter, volume fraction, and bulk temperature, all have a significant impact on the effective thermal conductivity of these suspensions. The 6% volume fraction of CuO nanoparticle/distilled water suspension resulted in an increase in the effective thermal conductivity of 1.52 times that of pure distilled water and the 10% Al2O3 nanoparticle/distilled water suspension increased the effective thermal conductivity by a factor of 1.3, at a temperature of 34°C. A two-factor ...

The importance of vertical and shared leadership within new venture top management teams: Implications for the performance of startups ☆

Abstract: The current study investigated the relative influence of vertical versus shared leadership within new venture top management teams on the performance of startups using two different samples. Vertical leadership stems from an appointed or formal leader of a team (e.g., the CEO), whereas shared leadership is a form of distributed leadership stemming from within a team. Transformational, transactional, empowering, and directive dimensions of both vertical and shared leadership were examined. New venture performance was considered in terms of revenue growth and employee growth. The first sample was comprised of 66 top management teams of firms drawn from Inc. Magazine's annual list of America's 500 fastest growing startups. The seconded sample consisted of 154 top management teams of startups randomly drawn from Dun and Bradstreet, which compiles the most extensive database available for identifying relatively young American-based ventures. Both vertical and shared leadership were found to be highly significant predictors of new venture performance. Further, hierarchical regression analysis found the shared leadership variables to account for a significant amount of variance in new venture performance beyond the vertical leadership variables. These results were consistent across both samples, thus providing robust evidence for the value of shared leadership, in addition to the more traditional concept of vertical leadership.

Coherent Control of THz Wave Generation in Ambient Air

Abstract: Our study of THz wave generation in the pulsed laser induced air plasma with individually controlled phase, polarization, and amplitude of the optical fundamental wave (omega) and its second harmonic (2omega) indicates that the third-order nonlinear optical process mixing the omega and 2omega beams in the ionized plasma is the main mechanism of the efficient THz wave generation. The polarity and the strength of the emitted THz field are completely controlled by the relative phase between the omega and 2omega waves. The measured THz field amplitude is proportional to the pulse energy of the fundamental beam and to the square root of the pulse energy of the second-harmonic beam once the total optical pulse energy exceeds the plasma formation threshold. The optimal THz field is achieved when all waves (omega, 2omega, and THz waves) are at the same polarization in the four-wave-mixing process.

TitaniQ: a titanium-in-quartz geothermometer

Abstract: Titanium is one of many trace elements to substitute for silicon in the mineral quartz. Here, we describe the temperature dependence of that substitution, in the form of a new geothermometer. To calibrate the “TitaniQ” thermometer, we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt, at temperatures ranging from 600 to 1,000°C, at 1.0 GPa. The Ti contents of quartz (in ppm by weight) from 13 experiments increase exponentially with reciprocal T as described by: $$ {\text{Log}}{\left( {X^{{{\text{qtz}}}}_{{{\text{Ti}}}} } \right)} = (5.69 \pm 0.02) - \frac{{(3765 \pm 24)}} {{T(K)}}. $$ Application of this thermometer is straightforward, typically requiring analysis of only one phase (quartz). This can be accomplished either by EPMA for crystallization temperatures above 600°C, or by SIMS for temperatures down to at least 400°. Resulting temperature estimates are very precise (usually better than ±5°C), potentially allowing detailed characterization of thermal histories within individual quartz grains. Although calibrated for quartz crystallized in the presence of rutile, the thermometer can also be applied to rutile-absent systems if TiO2 activity is constrained.

Inkjet Printing of Electrically Conductive Patterns of Carbon Nanotubes

Abstract: The advantageous physical properties of carbon nanotubes (CNTs), such as excellent thermal conductivity, good mechanical strength, optional semiconducting/metallic nature, and advanced field-emission behavior, have been utilized in a number of different devices for several years. The area-selective synthesis of well-organized CNTs on prepatterned growth templates using either catalytic or plasma-enhanced chemical vapor deposition methods (CCVD and PECVD, respectively) opens up further novel fields for advanced future applications. However, these promising techniques require complex lithography processes and sophisticated deposition facilities (PECVD) or are limited to thermally durable growth substrates (CCVD). Recent advances in nanotube chemistry enable both the dissolution and dispersion of CNTs in various solvents. These results suggest new alternatives for fabricating CNT patterns by simply dispensing/printing the dissolved/dispersed particles on substrates. Alternatively, controlled flocculation of CNT suspensions in flow channels or on prepatterned stamps can be accomplished to produce patterns of nanotubes on various surfaces. Herein, a cost-effective and scaleable deposition method for generating conductive multi-walled carbon nanotube (MWCNT) patterns on paper and polymer surfaces is presented. MWCNTs grown by CCVD were chemically modified to make the nanotubes dispersible in water, and in turn the aqueous dispersion was dispensed on various substrates using a commercial desktop inkjet printer. The electrical behavior of the printed patterns is investigated and the limitations of the process are discussed. For functionalization (Figure 1a), the MWCNTs were first refluxed in nitric acid to produce carboxyl, hydroxyl, and carbonyl groups at the defect sites of the outer graphene layer of the nanotubes. In a subsequent step, these hydroxyl and carbonyl groups were oxidized further with potassium permanganate solution (in perchloric acid) to achieve additional carboxyl groups on the surfaces of the nanotubes. Modifications of the as-grown CNT structure may be identified by comparison of the Raman spectra ACHTUNGTRENNUNGof the as-produced nanotubes (Figure 1b) and the fully ACHTUNGTRENNUNGfunctionalized nanotubes (Figure 1c) in the vicinity of the

A Faint New Milky Way Satellite in Bootes

Abstract: We announce the discovery of a new satellite of the Milky Way in the constellation of Bootes at a distance of ~60 kpc. It was found in a systematic search for stellar overdensities in the north Galactic cap using Sloan Digital Sky Survey Data Release 5. The color-magnitude diagram shows a well-defined turnoff, red giant branch, and extended horizontal branch. Its absolute magnitude is MV ~ -5.8 mag, which makes it one of the faintest galaxies known. The half-light radius is ~220 pc. The isodensity contours are elongated and have an irregular shape, suggesting that Boo may be a disrupted dwarf spheroidal galaxy.

Direct growth of aligned carbon nanotubes on bulk metals

Abstract: There are several advantages of growing carbon nanotubes (CNTs) directly on bulk metals, for example in the formation of robust CNT-metal contacts during growth. Usually, aligned CNTs are grown either by using thin catalyst layers predeposited on substrates or through vapour-phase catalyst delivery. The latter method, although flexible, is unsuitable for growing CNTs directly on metallic substrates. Here we report on the growth of aligned multiwalled CNTs on a metallic alloy, Inconel 600 (Inconel), using vapour-phase catalyst delivery. The CNTs are well anchored to the substrate and show excellent electrical contact with it. These CNT-metal structures were then used to fabricate double-layer capacitors and field-emitter devices, which demonstrated improved performance over previously designed CNT structures. Inconel coatings can also be used to grow CNTs on other metallic substrates. This finding overcomes the substrate limitation for nanotube growth which should assist the development of future CNT-related technologies.

An experimental study of contact effects in organic thin film transistors

Abstract: We report on parasitic contact effects in organic thin film transistors (OTFTs) fabricated with pentacene films. The influence on the OTFT performance of the source and drain contact metal and the device design was investigated. Top contact (TC) and bottom contact (BC) gated transmission line model (gated-TLM) test structures were used to extract the combined parasitic contact resistance as a function of gate voltage swing and drain-source voltage for OTFTs with gold source and drain contacts. For comparison BC test structures with palladium contacts were studied. Differences in the bias dependence of the contact resistance for TC and BC OTFTs indicate that charge injection and device performance are strongly affected by the device design and processing. The results from this investigation show that TC and BC device performances may be contact limited for high mobility OTFTs with channel lengths less than 10μm.

The anatomy of a power grid blackout - Root causes and dynamics of recent major blackouts

Abstract: This paper examines some of the more recent major blackouts and discusses some of the root causes and dynamics of these events. The paper aims to identify high-level conclusions and recommendations for improving system dynamic performance and reducing the risk of such catastrophic events

Proclivity for Improvisation as a Predictor of Entrepreneurial Intentions

Abstract: This study examines the relationship between improvisation and entrepreneurial intentions. Of specific interest is whether or not a proclivity for improvisation explains any variance in entrepreneurial intentions beyond what is accounted for by other relevant individual difference measures. Using a sample of 430 college students, entrepreneurial intentions are found to be significantly associated with measures of personality, motivation, cognitive style, social models, and improvisation. The strongest relationship is found between entrepreneurial intentions and improvisation. The results of hierarchical regression show that improvisation accounts for a significant amount of variance in entrepreneurial intention above and beyond what is accounted for by the other variables.

A New Milky Way Dwarf Satellite in Canes Venatici

Abstract: In this Letter, we announce the discovery of a new dwarf satellite of the Milky Way, located in the constellation Canes Venatici. It was found as a stellar overdensity in the north Galactic cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The satellite's color-magnitude diagram shows a well-defined red giant branch as well as a horizontal branch. As judged from the tip of the red giant branch, it lies at a distance of ~220 kpc. Based on the SDSS data, we estimate an absolute magnitude of MV ~ -7.9, a central surface brightness of μ0, V ~ 28 mag arcsec-2, and a half-light radius of ~85 (~550 pc at the measured distance). The outer regions of Canes Venatici appear extended and distorted. The discovery of such a faint galaxy in proximity to the Milky Way strongly suggests that more such objects remain to be found.

Detection of broadband terahertz waves with a laser-induced plasma in gases.

Abstract: We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.

Plate-boundary deformation associated with the great Sumatra–Andaman earthquake

Abstract: The Sumatra–Andaman earthquake of 26 December 2004 is the first giant earthquake (moment magnitude M_w > 9.0) to have occurred since the advent of modern space-based geodesy and broadband seismology. It therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events. Here we report estimates of the ground displacement associated with this event, using near-field Global Positioning System (GPS) surveys in northwestern Sumatra combined with in situ and remote observations of the vertical motion of coral reefs. These data show that the earthquake was generated by rupture of the Sunda subduction megathrust over a distance of >1,500 kilometres and a width of <150 kilometres. Megathrust slip exceeded 20 metres offshore northern Sumatra, mostly at depths shallower than 30 kilometres. Comparison of the geodetically and seismically inferred slip distribution indicates that ~30 per cent additional fault slip accrued in the 1.5 months following the 500-second-long seismic rupture. Both seismic and aseismic slip before our re-occupation of GPS sites occurred on the shallow portion of the megathrust, where the large Aceh tsunami originated. Slip tapers off abruptly along strike beneath Simeulue Island at the southeastern edge of the rupture, where the earthquake nucleated and where an M_w = 7.2 earthquake occurred in late 2002. This edge also abuts the northern limit of slip in the 28 March 2005 M_w = 8.7 Nias–Simeulue earthquake.

A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in the Third Data Release of the Sloan Digital Sky Survey

Abstract: We perform an analysis of spectra and photometry for 22,770 stars included in the third data release (DR3) of the Sloan Digital Sky Survey (SDSS). We measure radial velocities and, based on a model-atmosphere analysis, derive estimates of the atmospheric parameters (effective temperature, surface gravity, and [Fe/H]) for each star. Stellar evolution models are then used to estimate distances. We thoroughly check our analysis procedures using three recently published spectroscopic libraries of nearby stars, and compare our results with those obtained from alternative approaches. The SDSS sample covers a range in stellar brightness of 14 < V < 22, primarily at intermediate galactic latitudes, and comprises large numbers of F- and G-type stars from the thick-disk and halo populations (up to 100 kpc from the galactic plane), therefore including some of the oldest stars in the Milky Way. In agreement with previous results from the literature, we find that halo stars exhibit a broad range of iron abundances, with a peak at [Fe/H] {approx_equal} -1.4. This population exhibits essentially no galactic rotation. Thick-disk G-dwarf stars at distances from the galactic plane in the range 1 < |z| < 3 kpc show a much more compact metallicity distribution, with a maximummore » at [Fe/H] {approx_equal} -0.7, and a median galactic rotation velocity at that metallicity of 157 {+-} 4 km s{sup -1} (a lag relative to the thin disk of 63 km s{sup -1}). SDSS DR3 includes spectra of many F-type dwarfs and subgiants between 1 and 3 kpc from the plane with galactic rotation velocities consistent with halo membership. A comparison of color indices and metal abundances with isochrones indicates that no significant star formation has taken place in the halo in the last {approx} 11 Gyr, but there are thick-disk stars which are at least 2 Gyr younger. We find the metallicities of thick-disk stars to be nearly independent of galactocentric distance between 5 and 14 kpc from the galactic center, in contrast with the marked gradients found in the literature for the thin disk. No vertical metallicity gradient is apparent for the thick disk, but we detect a gradient in its rotational velocity of -16 {+-} 4 km s{sup -1} kpc{sup -1} between 1 and 3 kpc from the plane. We estimate that among the stars in our sample there are over 2000 with an iron abundance [Fe/H] < -2, and over 150 stars with an iron abundance [Fe/H] < -3.« less

Coverage by directional sensors in randomly deployed wireless sensor networks

Abstract: We study a novel “coverage by directional sensors” problem with tunable orientations on a set of discrete targets. We propose a Maximum Coverage with Minimum Sensors (MCMS) problem in which coverage in terms of the number of targets to be covered is maximized whereas the number of sensors to be activated is minimized. We present its exact Integer Linear Programming (ILP) formulation and an approximate (but computationally efficient) centralized greedy algorithm (CGA) solution. These centralized solutions are used as baselines for comparison. Then we provide a distributed greedy algorithm (DGA) solution. By incorporating a measure of the sensors residual energy into DGA, we further develop a Sensing Neighborhood Cooperative Sleeping (SNCS) protocol which performs adaptive scheduling on a larger time scale. Finally, we evaluate the properties of the proposed solutions and protocols in terms of providing coverage and maximizing network lifetime through extensive simulations. Moreover, for the case of circular coverage, we compare against the best known existing coverage algorithm.

Effect of aggregation on thermal conduction in colloidal nanofluids

Abstract: Using effective medium theory the authors demonstrate that the thermal conductivity of nanofluids can be significantly enhanced by the aggregation of nanoparticles into clusters. Predictions of the effective medium theory are in excellent agreement with detailed numerical calculation on model nanofluids involving fractal clusters and show the importance of cluster morphology on thermal conductivity enhancements.

A Curious Milky Way Satellite in Ursa Major

Abstract: In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram (CMD) shows a well-defined subgiant branch, main sequence, and turnoff, from which we estimate a distance of ~30 kpc and a projected size of ~250 × 125 pc2. The CMD suggests a composite population with some range in metallicity and/or age. Based on its extent and stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named Ursa Major II (UMa II) after its constellation. Using SDSS data, we find an absolute magnitude of MV ~ -3.8, which would make it the faintest known satellite galaxy. UMa II's isophotes are irregular and distorted with evidence for multiple concentrations; this suggests that the satellite is in the process of disruption.