Showing papers by "University of Victoria published in 2007"

“Vygotsky’s Neglected Legacy”: Cultural-Historical Activity Theory:

Abstract: The authors describe an evolving theoretical framework that has been called one of the best kept secrets of academia: cultural-historical activity theory, the result of proposals Lev Vygotsky first articulated but that his students and followers substantially developed to constitute much expanded forms in its second and third generations. Besides showing that activity theory transforms how research should proceed regarding language, language learning, and literacy in particular, the authors demonstrate how it is a theory for praxis, thereby offering the potential to overcome some of the most profound problems that have plagued both educational theorizing and practice.

Customer Value Creation: A Practical Framework

Abstract: Creation of value for customers is a critical task for marketers, particularly when developing new products and services or starting new businesses. This paper presents a new conceptual framework for marketers to ponder when exploring ways to distinguish themselves, in the eyes of the customer, from others in the marketplace. This framework is built on the strengths of existing frameworks. Possible applications of the framework in designing marketing strategy, recognizing new product opportunities, and enhancing product concept specifications are discussed.

SALT2: using distant supernovae to improve the use of type Ia supernovae as distance indicators

Abstract: We present an empirical model of Type Ia supernovae spectro-photometric evolution with time. The model is built using a large data set including light-curves and spectra of both nearby and distant supernovae, the latter being observed by the SNLS collaboration. We derive the average spectral sequence of Type Ia supernovae and their main variability components including a color variation law. The model allows us to measure distance moduli in the spectral range 2500-8000 A with calculable uncertainties, including those arising from variability of spectral features. Thanks to the use of high-redshift SNe to model the rest-frame UV spectral energy distribution, we are able to derive improved distance estimates for SNe Ia in the redshift range 0.8

The statistics of Λ CDM halo concentrations

Abstract: We use the Millennium Simulation (MS) to study the statistics of A cold dark matter (ACDM) halo concentrations at z = 0. Our results confirm that the average halo concentration declines monotonically with mass; the concentration-mass relation is well fitted by a power law over three decades in mass, up to the most massive objects that form in a ACDM universe (∼ 10 15 h -1 M ⊙ ). This is in clear disagreement with the predictions of the model proposed by Bullock et al. for these rare objects, and agrees better with the original predictions of Navarro, Frenk & White. The large volume surveyed, together with the unprecedented numerical resolution of the MS, allows us to estimate with confidence the distribution of concentrations and, consequently, the abundance of systems with unusual properties. About one in a hundred cluster haloes (M 200 ≥ 3 x 10 14 h -1 M ⊙ ) have concentrations exceeding c 200 = 7.5, a result that may be useful in interpreting the likelihood of unusually strong massive gravitational lenses, such as Abell 1689, in the ACDM cosmogony. A similar fraction of about 1 per cent of galaxy-sized haloes (M 200 ∼ 10 12 h -1 M ⊙ ) have c 200 < 4.5 and this could be relevant to models that attempt to reconcile the ACDM cosmology with rotation curves of low surface brightness galaxies by appealing to haloes of unexpectedly low concentration. We find that halo concentrations are independent of spin once haloes manifestly out of equilibrium have been removed from the sample. Compared to their relaxed brethren, the concentrations of out-of-equilibrium haloes tend to be lower and have more scatter, while their spins tend to be higher. A number of previously noted trends within the halo population are induced primarily by these properties of unrelaxed systems. Finally, we compare the result of predicting halo concentrations using the mass assembly history of the main progenitor with predictions based on simple arguments regarding the assembly time of all progenitors. The latter are typically as good or better than the former, suggesting that halo concentration depends not only on the evolutionary path of a halo's main progenitor, but on how and when all of its constituents collapsed to form non-linear objects.

The Central Question in Entrepreneurial Cognition Research 2007

Abstract: In this article, we take note of advances in the entrepreneurial cognition research stream. In doing so, we bring increasing attention to the usefulness of entrepreneurial cognition research. First, we offer and develop a central research question to further enable entrepreneurial cognition inquiry. Second, we present the conceptual background and some representative approaches to entrepreneurial cognition research that form the context for this question. Third, we introduce the articles in this Special Issue as framed by the central question and approaches to entrepreneurial cognition research, and suggest how they further contribute to this developing stream. Finally, we offer our views concerning the challenges and opportunities that await the next generation of entrepreneurial cognition scholarship. We therefore invite (and seek to enable) the growing community of entrepreneurship researchers from across multiple disciplines to further develop the “thinking– doing” link in entrepreneurship research. It is our goal to offer colleagues an effective research staging point from which they may embark upon many additional research expeditions and investigations involving entrepreneurial cognition.

The statistics of LCDM Halo Concentrations

Abstract: We use the Millennium Simulation (MS) to study the statistics of LCDM halo concentrations at z = 0. Our results confirm that the average halo concentration declines monotonically with mass; a power-law fits well the concentration-mass relation for over 3 decades in mass, up to the most massive objects to form in a LCDM universe (~ 10^15 h^-1 Msol). This is in clear disagreement with the predictions of the model proposed by Bullock et al. for these rare objects, and agrees better with the original predictions of Navarro, Frenk, & White. The large volume surveyed, together with the unprecedented numerical resolution of the MS, allow us to estimate with confidence the distribution of concentrations and, consequently, the abundance of systems with unusual properties. About one in a hundred cluster haloes (M200 >~ 3x10^14 h^-1 Msol) have concentrations exceeding c200 = 7.5, a result that may be used to interpret the likelihood of unusually strong massive gravitational lenses, such as Abell 1689, in the LCDM cosmogony. A similar fraction (1 in 100) of galaxy-sized haloes (M200 ~ 10^12 h^-1 Msol) have c200 < 4.5, an important constraint on models that attempt to reconcile the rotation curves of low surface-brightness galaxies by appealing to haloes of unexpectedly low concentration. We find that halo concentrations are independent of spin once haloes manifestly out of equilibrium are removed from the sample. Compared to their relaxed brethren, the concentrations of out-of-equilibrium haloes tend to be lower and to have more scatter, while their spins tend to be higher... (continue)

The All-Wavelength Extended Groth Strip International Survey(AEGIS) Data Sets

Abstract: In this the first of a series of Letters, we present a panchromatic data set in the Extended Groth Strip region of the sky. Our survey, the All-Wavelength Extended Groth Strip International Survey (AEGIS), aims to study the physical properties and evolutionary processes of galaxies at z ~ 1. It includes the following deep, wide-field imaging data sets: Chandra/ACIS X-ray, GALEX ultraviolet, CFHT/MegaCam Legacy Survey optical, CFHT/CFH12K optical, Hubble Space Telescope/ACS optical and NICMOS near-infrared, Palomar/WIRC near-infrared, Spitzer/IRAC mid-infrared, Spitzer/MIPS far-infrared, and VLA radio continuum. In addition, this region of the sky has been targeted for extensive spectroscopy using the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II 10 m telescope. Our survey is compared to other large multiwavelength surveys in terms of depth and sky coverage.

The RAVE survey: constraining the local Galactic escape speed

Abstract: We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high-velocity stars from the RAVE survey and two previously published data sets. We use cosmological simulations of disc galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range 498

Subjects of Empire: Indigenous Peoples and the ‘Politics of Recognition’ in Canada

Abstract: Over the last 30 years, the self-determination efforts and objectives of Indigenous peoples in Canada have increasingly been cast in the language of ‘recognition’ — recognition of cultural distinctiveness, recognition of an inherent right to self-government, recognition of state treaty obligations, and so on. In addition, the last 15 years have witnessed a proliferation of theoretical work aimed at fleshing out the ethical, legal and political significance of these types of claims. Subsequently, ‘recognition’ has now come to occupy a central place in our efforts to comprehend what is at stake in contestations over identity and difference in colonial contexts more generally. In this paper, I employ Frantz Fanon's critique of Hegel's master–slave dialectic to challenge the now hegemonic assumption that the structure of domination that frames Indigenous–state relations in Canada can be undermined via a liberal politics of recognition. Against this assumption, I argue that instead of ushering in an era of peaceful coexistence grounded on the Hegelian ideal of reciprocity, the contemporary politics of recognition promises to reproduce the very configurations of colonial power that Indigenous demands for recognition have historically sought to transcend.

It's worse than you thought: The feedback negativity and violations of reward prediction in gambling tasks

Abstract: The reinforcement learning theory suggests that the feedback negativity should be larger when feedback is unexpected. Two recent studies found, however, that the feedback negativity was unaffected by outcome probability. To further examine this issue, participants in the present studies made reward predictions on each trial of a gambling task where objective reward probability was indicated by a cue. In Study 1, participants made reward predictions following the cue, but prior to their gambling choice; in Study 2, predictions were made following their gambling choice. Predicted and unpredicted outcomes were associated with equivalent feedback negativities in Study 1. In Study 2, however, the feedback negativity was larger for unpredicted outcomes. These data suggest that the magnitude of the feedback negativity is sensitive to violations of reward prediction, but that this effect may depend on the close coupling of prediction and outcome.

The spin and shape of dark matter haloes in the Millennium simulation of a Λ cold dark matter universe

Abstract: We investigate the spins and shapes of over a million dark matter haloes identified at z = 0 in the Millennium simulation. Our sample spans halo masses ranging from dwarf galaxies to rich galaxy clusters. The very large dynamic range of this A cold dark matter cosmological simulation enables the distribution of spins and shapes and their variation with halo mass and environment to be characterized with unprecedented precision. We compare results for haloes identified using three different algorithms, and investigate (and remove) biases in the estimate of angular momentum introduced both by the algorithm itself and by numerical effects. We introduce a novel halo definition called the TREE halo, based on the branches of the halo merger trees, which is more appropriate for comparison with real astronomical objects than the traditional 'friends-of-friends' and 'spherical overdensity' (SO) algorithms. We find that for this many objects, the traditional lognormal function is no longer an adequate description of the distribution, P(λ), of the dimensionless spin parameter λ, and we provide a different function that gives a better fit for TREE and SO haloes. The variation in spin with halo mass is weak but detectable, although the trend depends strongly on the halo definition used. For the entire population of haloes, we find median values of λ med = 0.0367-0.0429, depending on the definition of a halo. The haloes exhibit a range of shapes, with a preference for prolateness over oblateness. More-massive haloes tend to be less spherical and more prolate. We find that the more-spherical haloes have less coherent rotation in the median, and those closest to being spherical have a spin independent of mass (λ med ≈0.033). The most-massive haloes have a spin independent of shape (λ med ≈0.032). The majority of haloes have their angular momentum vector aligned with their minor axis and perpendicular to their major axis. We find a general trend for higher spin haloes to be more clustered, with a stronger effect for more-massive haloes. For galaxy cluster haloes, this can be larger than a factor of∼2.

Alliance networks and firm performance: The impact of repeated partnerships

Abstract: A phenomenon that has become the focus of recent research on interorganizational alliance network growth is that firms often enter into repeated relationships with prior partners. The implications of this tendency on corporate performance, however, are not well understood. From transaction cost and network perspectives, I test competing hypotheses on a large sample of multinational corporations. My results indicate clearly that firms not only often do enter into repeated equity-based partnerships but also that those with a greater propensity to do so experience inferior economic performance. Further, statistical tests indicate that the negative effect of repeated partnerships on performance is particularly strong in environments of greater technological uncertainty. Copyright © 2007 John Wiley & Sons, Ltd.

What's new in stable radical chemistry?

Abstract: Many kinds of radicals are stable enough to isolate, handle, and store without any special precautions. The diversity in molecular architectures of these stable radicals is sufficiently large that the common factors governing radical stability/persistence, geometric and electronic structure, association/dimerization preferences, and reactivity have generally not been well articulated or appreciated. This review provides a survey of the major classes of stable or persistent organic/organomain group radicals with a view to presenting a unified description of the interdependencies between radical molecular structure and properties.

The Haunted Halos of Andromeda and Triangulum: A Panorama of Galaxy Formation in Action*

Abstract: We present a deep photometric survey of the Andromeda galaxy, conducted with the wide-field cameras of the CFHT and INT telescopes. The surveyed area covers the inner 50kpc of the galaxy and the Southern quadrant out to a projected distance of ∼ 150kpc. A survey extension to M33 at > 200kpc probes the interface between the halos of these two galaxies. This survey is the first systematic panoramic study of this very outermost region of galaxies. We detect a multitude of largescale structures of low surface brightness, including several streams. Significant variations in stellar populations due to intervening stream-like structures are detected in the inner halo along the minor axis. This, together with the fact that the light profile between 0 ◦ .5 < R < 1 ◦ .3 follows the exponential “extended disk”, is particularly important in shedding light on the mixed and sometimes conflicting results reported in previous studies. Two new relatively luminous (MV ∼ −9) dwarf galaxies And XV and XVI are found in the study; And XVI is a particularly interesting specimen being located 270kpc in front of M31, towards the Milky Way. Underlying the many substructures that we have uncovered lies a faint, smooth and extremely extended halo component, reaching out to 150 kpc, whose stellar populations are predominantly metal-poor. This is consistent with recent claims based on spectroscopy of a small sample of stars. We find that the smooth halo component in M31 has a radially-decreasing profile that can be fit with a Hernquist model of immense scale radius ∼ 55kpc, almost a factor

The Shear TEsting Programme 2: Factors affecting high precision weak lensing analyses

Abstract: The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known shear signal. We determine the common features of algorithms that most successfully recover the input parameters. A desirable goal would be the combination of their best elements into one ultimate shear-measurement method. In this analysis, we achieve previously unattained discriminatory precision via a combination of more extensive simulations and pairs of galaxy images that have been rotated with respect to each other. That removes the otherwise overwhelming noise from their intrinsic ellipticities. Finally, the robustness of our simulation approach is confirmed by testing the relative calibration of methods on real data. Weak-lensing measurements have improved since the first STEP paper. Several methods now consistently achieve better than 2 per cent precision, and are still being developed. However, we can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative shear calibration bias: not least because this cannot be internally calibrated with real data. We determine which galaxy populations are responsible for bias and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. The simulated point spread functions are not allowed to vary spatially, to avoid additional confusion from interpolation errors. We have isolated several previously unrecognized aspects of galaxy shape measurement, in which focused development could provide further progress towards the sub-per cent level of precision desired for future surveys. These areas include the suitable treatment of image pixellization and galaxy morphology evolution. Ignoring the former effect affects the measurement of shear in different directions, leading to an overall underestimation of shear and hence the amplitude of the matter power spectrum. Ignoring the second effect could affect the calibration of shear estimators as a function of galaxy redshift, and the evolution of the lensing signal, which will be vital to measure parameters including the dark energy equation of state.

A New Biometric Technology Based on Mouse Dynamics

Abstract: In this paper, we introduce a new form of behavioral biometrics based on mouse dynamics, which can be used in different security applications. We develop a technique that can be used to model the behavioral characteristics from the captured data using artificial neural networks. In addition, we present an architecture and implementation for the detector, which cover all the phases of the biometric data flow including the detection process. Experimental data illustrating the experiments conducted to evaluate the accuracy of the proposed detection technique are presented and analyzed. Specifically, three series of experiments are conducted. The main experiment, in which 22 participants are involved, reproduces real operating conditions in computing systems by giving participants an individual choice of operating environments and applications; 284 hours of raw mouse data are collected over 998 sessions, with an average of 45 sessions per user. The two other experiments, involving seven participants, provided a basis for studying the confounding factors arising from the main experiment by fixing the environment variables. In the main experiment, the performance results presented using receiver operating characteristic (ROC) curves and a confusion matrix yield at the crossover point (that is, the threshold set for an equal error rate) a false acceptance rate (FAR) of 2.4649 percent and a false rejection rate (FRR) of 2.4614 percent.

The efficiency of a turbine in a tidal channel

Abstract: There is an upper bound to the amount of power that can be generated by turbines in tidal channels as too many turbines merely block the flow. One condition for achievement of the upper bound is that the turbines are deployed uniformly across the channel, with all the flow through them, but this may interfere with other uses of the channel. An isolated turbine is more effective in a channel than in an unbounded flow, but the current downstream is non-uniform between the wake of the turbines and the free stream. Hence some energy is lost when these streams merge, as may occur in a long channel. We show here, for ideal turbine models, that the fractional power loss increases from 1/3 to 2/3 as the fraction of the channel cross-section spanned by the turbines increases from 0 to close to 1. In another scenario, possibly appropriate for a short channel, the speed of the free stream outside the turbine wake is controlled by separation at the channel exit. In this case, the maximum power obtainable is slightly less than proportional to the fraction of the channel cross-section occupied by turbines.

Multifactorial and functional mobility assessment tools for fall risk among older adults in community, home-support, long-term and acute care settings

Abstract: Objective: to conduct a systematic review of published studies that test the validity and reliability of fall-risk assessmenttools for use among older adults in community, home-support, long-term and acute care settings Methods: searches were conducted in EbscoHost and MEDLINE for published studies in the English language between January 1980 and July 2004, where the primary or secondary purpose was to test the predictive value of one or more fall assessmenttools on a population primarily 65 years and older Thetoolmust have had as its primary outcome falls, fall-related injury or gait/balance Only studies that used prospective validation were considered Findings:thirty-four articlestesting38 differenttools met the inclusioncriteriaThe community settingrepresentsthe largest number of studies (14) and tools (23) tested, followed by acute (12 studies and 8 tools), long-term care (LTC) (6 studies and 10 tools) and home-support (4 studies and 4 tools) Eleven of the 38 tools are multifactorial assessment tools (MAT) that cover a wide range of fall-risk factors, and 27 are functional mobility assessment tools (FMA) that involve measures of physical activity related to gait, strength or balance Conclusion: fall-risk assessment tools exist that show moderate to good validity and reliability in most health service delivery areas However, few tools were tested more than once or in more than one setting Therefore, no single tool can be recommended for implementation in all settings or for all subpopulations within each setting

K-corrections and spectral templates of Type Ia supernovae

Abstract: With the advent of large dedicated Type Ia supernova (SN Ia) surveys, K-corrections of SNe Ia and their uncertainties have become especially important in the determination of cosmological parameters. While K-corrections are largely driven by SN Ia broadband colors, it is shown here that the diversity in spectral features of SNe Ia can also be important. For an individual observation, the statistical errors from the inhomogeneity in spectral features range from 0.01 (where the observed and rest-frame filters are aligned) to 0.04 (where the observed and rest-frame filters are misaligned). To minimize the systematic errors caused by an assumed SN Ia spectral energy distribution (SED), we outline a prescription for deriving a mean spectral template time series that incorporates a large and heterogeneous sample of observed spectra. We then remove the effects of broadband colors and measure the remaining uncertainties in the K-corrections associated with the diversity in spectral features. Finally, we present a template spectroscopic sequence near maximum light for further improvement on the K-correction estimate. A library of ~;;600 observed spectra of ~;;100 SNe Ia from heterogeneous sources is used for the analysis.

The Francisella pathogenicity island protein IglA localizes to the bacterial cytoplasm and is needed for intracellular growth

Abstract: Background Francisella tularensis is a gram negative, facultative intracellular bacterium that is the etiological agent of tularemia. F. novicida is closely related to F. tularensis but has low virulence for humans while being highly virulent in mice. IglA is a 21 kDa protein encoded by a gene that is part of an iglABCD operon located on the Francisella pathogenicity island (FPI).

Reward prediction error signals associated with a modified time estimation task.

Abstract: The feedback error-related negativity (fERN) is a component of the human event-related brain potential (ERP) elicited by feedback stimuli. A recent theory holds that the fERN indexes a reward prediction error signal associated with the adaptive modification of behavior. Here we present behavioral and ERP data recorded from participants engaged in a modified time estimation task. As predicted by the theory, our results indicate that fERN amplitude reflects a reward prediction error signal and that the size of this error signal is correlated across participants with changes in task performance.

Sickness Presenteeism, Sickness Absenteeism, and Health Following Restructuring in a Public Service Organization

Abstract: This study examined the relationship between sickness presenteeism, sickness absenteeism, organizational outcomes and employee health. In particular, we wanted to investigate to what degree employees were substituting sickness presence for sickness absence. Three hypotheses were tested to formalize this ‘substitution proposition’. We surveyed a Canadian public service organization which was involved in a large scale downsizing initiative. For this study, 237 Personnel Corporation (pseudonym used) employees responded to the survey, representing a 66 per cent response rate. Survey results indicated that, while the workforce was of average health, sickness absenteeism was less than half that of the national average. The difference could be accounted for by sickness presenteeism – the average number of days employees attended work while ill or injured was greater than the number of days of sickness absence. The pattern of results supported the notion that employees were substituting presenteeism for absenteeism. The frequency and type of self-reported health problems were highly similar for presenteeism and absenteeism. Work factors (e.g. job security, supervisor support and job satisfaction) tested were significantly correlated with presenteeism. Presenteeism appears to be a stronger predictor of health than absenteeism, suggesting that efforts to improve workplace health may have a more immediate impact on presenteeism than on absenteeism.

The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action

Abstract: We present a deep photometric survey of M31, conducted with the CFHT and INT, covering the inner 50 kpc of the galaxy, the Southern quadrant out to 150 kpc, and extending to M33. This is the first systematic panoramic study of this very outermost region of galaxies. We detect several streams and other large-scale structures, and two new dwarf galaxies: And XV and XVI. The discovery of substructure on the minor axis, together with the fact that the light profile between 0.5 < R < 1.3 follows the exponential ``extended disk'', is particularly important in shedding light on the mixed and sometimes conflicting results reported in previous studies. Underlying the substructures lies a faint, metal-poor, smooth and extremely extended halo, reaching out to at least 150 kpc. The smooth halo component in M31 has a profile that can be fit with a Hernquist model of immense scale radius ~55 kpc, almost a factor of 4 larger than theoretical predictions. Alternatively a power-law with exponent -1.91 +/- 0.11 can be fit to the profile. The total luminosity of this structure is similar to that of the halo of the Milky Way. This vast, smooth, underlying halo is reminiscent of a classical monolithic model and completely unexpected from modern galaxy formation models. M33 is also found to have an extended metal-poor halo component, which can be fit with a Hernquist model also of scale radius ~55 kpc. These extended slowly-decreasing halos will provide a challenge and strong constraints for further modeling. [Abridged]

A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies

Abstract: We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Bootes, Ursa Major I, Ursa Major II and Willman 1 (Will). Using the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have obtained samples that contain from ∼ 15 to ∼85 probable members of these satellites for which we derive radial velocities precise to a few km s -1 down to i ∼ 21-22. About half of these stars are observed with a high enough signal-to-noise ratio to estimate their metallicity to within ±0.2 dex. The characteristics of all the observed stars are made available, along with those of the Canes Venatici I dwarf galaxy that have been analysed in a companion paper. From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (υ r = 115 ± 5kms -1 ) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Will object is not a globular cluster given its metallicity scatter over -2.0 ≤ [Fe/H] ≤ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3 +2.3-1.3 km s -1 around a systemic velocity of -12.3 ± 2.3 km s -1 which implies a mass-to-light ratio of ∼700 and a total mass of ∼5 x 10 5 M O for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10 7 M O limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.

Synthetic ion channels in bilayer membranes

Abstract: Natural ion channels are large protein complexes that regulate key functions of cells. Supramolecular chemists have been able to take hints from Nature to design and prepare completely synthetic ion channel systems that reproduce many of the fundamental functions of natural channels. This tutorial review introduces the field to non-specialists. It examines the design, synthesis, incorporation, and characterization of synthetic ion channels in bilayer membranes, and points to potential applications of synthetic ion channels.

Particle physics catalysis of thermal big bang nucleosynthesis.

Abstract: We point out that the existence of metastable, $\ensuremath{\tau}g{10}^{3}\text{ }\text{ }\mathrm{s}$, negatively charged electroweak-scale particles (${X}^{\ensuremath{-}}$) alters the predictions for lithium and other primordial elemental abundances for $Ag4$ via the formation of bound states with nuclei during big bang nucleosynthesis. In particular, we show that the bound states of ${X}^{\ensuremath{-}}$ with helium, formed at temperatures of about $T={10}^{8}\text{ }\text{ }\mathrm{K}$, lead to the catalytic enhancement of $^{6}\mathrm{Li}$ production, which is 8 orders of magnitude more efficient than the standard channel. In particle physics models where subsequent decay of ${X}^{\ensuremath{-}}$ does not lead to large nonthermal big bang nucleosynthesis effects, this directly translates to the level of sensitivity to the number density of long-lived ${X}^{\ensuremath{-}}$ particles ($\ensuremath{\tau}g{10}^{5}\text{ }\text{ }\mathrm{s}$) relative to entropy of ${n}_{{X}^{\ensuremath{-}}}/s\ensuremath{\lesssim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$, which is one of the most stringent probes of electroweak scale remnants known to date.