45,336 research outputs found
Hydration and mobility of HO-(aq)
The hydroxide anion plays an essential role in many chemical and biochemical
reactions. But a molecular-scale description of its hydration state, and hence
also its transport, in water is currently controversial. The statistical
mechanical quasi-chemical theory of solutions suggests that HO[H2O]3- is the
predominant species in the aqueous phase under standard conditions. This result
is in close agreement with recent spectroscopic studies on hydroxide water
clusters, and with the available thermodynamic hydration free energies. In
contrast, a recent ab initio molecular dynamics simulation has suggested that
HO[H_2O]4- is the only dominant aqueous solution species. We apply adiabatic ab
initio molecular dynamics simulations, and find good agreement with both the
quasi-chemical theoretical predictions and experimental results. The present
results suggest a picture that is simpler, more traditional, but with
additional subtlety. These coordination structures are labile but the
tri-coordinate species is the prominent case. This conclusion is unaltered with
changes in the electronic density functional. No evidence is found for
rate-determining activated inter-conversion of a HO[H2O]4- trap structure to
HO[H2O]3-, mediating hydroxide transport. The view of HO- diffusion as the
hopping of a proton hole has substantial validity, the rate depending largely
on the dynamic disorder of the water hydrogen-bond network.Comment: 7 pages, 5 figures, additional results include
Super-Razor and Searches for Sleptons and Charginos at the LHC
Direct searches for electroweak pair production of new particles at the LHC
are a difficult proposition, due to the large background and low signal cross
sections. We demonstrate how these searches can be improved by a combination of
new razor variables and shape analysis of signal and background kinematics. We
assume that the pair-produced particles decay to charged leptons and missing
energy, either directly or through a W boson. In both cases the final state is
a pair of opposite sign leptons plus missing transverse energy. We estimate
exclusion reach in terms of sleptons and charginos as realized in minimal
supersymmetry. We compare this super-razor approach in detail to analyses based
on other kinematic variables, showing how the super-razor uses more of the
relevant kinematic information while achieving higher selection efficiency on
signals, including cases with compressed spectra.Comment: 33 pages, 33 figure
Laboratory observations of slow earthquakes and the spectrum of tectonic fault slip modes
Slow earthquakes represent an important conundrum in earthquake physics. While regular
earthquakes are catastrophic events with rupture velocities governed by elastic wave speed,
the processes that underlie slow fault slip phenomena, including recent discoveries of tremor,
slow-slip and low-frequency earthquakes, are less understood. Theoretical models and sparse
laboratory observations have provided insights, but the physics of slow fault rupture remain
enigmatic. Here we report on laboratory observations that illuminate the mechanics of
slow-slip phenomena. We show that a spectrum of slow-slip behaviours arises near the
threshold between stable and unstable failure, and is governed by frictional dynamics via the
interplay of fault frictional properties, effective normal stress and the elastic stiffness of the
surrounding material. This generalizable frictional mechanism may act in concert with other
hypothesized processes that damp dynamic ruptures, and is consistent with the broad range
of geologic environments where slow earthquakes are observed
Fast model predictive control for hydrogen outflow regulation in ethanol steam reformers
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In the recent years, the presence of alternative power sources, such as solar panels, wind farms, hydropumps
and hydrogen-based devices, has significantly increased. The reasons of this trend are clear: contributing to
a reduction of gas emissions and dependency on fossil fuels. Hydrogen-based devices are of particular interest due
to their significant efficiency and reliability. Reforming technologies are among the most economic and efficient ways
of producing hydrogen. In this paper we consider the regulation of hydrogen outflow in an ethanol steam reformer
(ESR). In particular, a fast model predictive control approach based on a finite step response model of the process
is proposed. Simulations performed using a more realistic non-linear model show the effectiveness of the proposed
approach in driving the ESR to different operating conditions while fulfilling input and output constraints.Peer ReviewedPostprint (author's final draft
Comparative Analysis Of Zebrafish And Planarian Model Systems For Developmental Neurotoxicity Screens Using An 87-Compound Library
There is a clear need to establish and validate new methodologies to more quickly and efficiently screen chemicals for potential toxic effects, particularly on development. The emergence of alternative animal systems for rapid toxicology screens presents valuable opportunities to evaluate how systems complement each other. In this article, we compare a chemical library of 87-compounds in two such systems, developing zebrafish and freshwater planarians, by screening for developmental neurotoxic effects. We show that the systems’ toxicological profiles are complementary to each other, with zebrafish yielding more detailed morphological endpoints and planarians more behavioral endpoints. Overall, zebrafish was more sensitive to this chemical library, yielding 86/87 hits, compared to 50/87 hits in planarians. The difference in sensitivity could not be attributed to molecular weight, Log Kow or the bioconcentration factor. Of the 87 chemicals, 28 had previously been evaluated in mammalian developmental neuro- (DNT), neuro- or developmental toxicity studies. Of the 28, 20 were hits in the planarian, and 27 were hits in zebrafish. Eighteen of the 28 had previously been identified as DNT hits in mammals and were highly associated with activity in zebrafish and planarian behavioral assays in this study. Only 1 chemical (out of 28) was a false negative in both zebrafish and planarian systems. Differences in endpoint coverage and system sensitivity illustrate the value of a dual systems approach to rapidly query a large chemical-bioactivity space and provide weight-of-evidence for prioritization of chemicals for further testing
Sp(4,R)/GL(2,R) Matrix Structure of Geodesic Solutions for Einstein--Maxwell--Dilaton--Axion Theory
The constructed matrix operator defines the family of
isotropic geodesic containing vacuum point lines in the target space of the
stationary D=4 Einstein--Maxwell--dilaton--axion theory. This operator is used
to derive a class of solutions which describes a point center system with
nontrivial values of mass, parameter NUT, as well as electric, magnetic,
dilaton and axion charges. It is shown that this class contains both particular
solutions Majumdar--Papapetrou--like black holes and massless asymptotically
nonflat naked singularities.Comment: 20 pages, RevTex, no figures, Submitted to Phys.Rev.
Reducing Stigma toward the Transgender Community: An Evaluation of a Humanizing and Perspective-Taking Intervention
Transgender (TG) individuals, or those whose gender identities, expressions and/or behaviors differ from their biological sex (Kirk & Kulkarni, 2006) feel there is a pervasive pattern of discrimination and prejudice directed toward them (Lombardi et al., 2001). In comparison to their heterosexual peers, LGBT youth and emerging adults are at increased risk for a host of adverse outcomes including: suicide, depression, harassment, and victimization (IOM, 2011).
Stigma has been characterized as encompassing several components: labeling, making an association between the label and a negative stereotype, separating those who are different as an “out-group” and discriminating. In a recent analysis of the transgender experience, Hill (2002) described three key constructs that can be used to understand negative emotions and behaviors toward transgender individuals: transphobia – an emotional disgust toward gender non-conforming individuals; genderism – a belief that gender non-conforming individuals are pathological or disordered; gender bashing – assault or harassment of gender non-conforming individuals.
Recent work on minority stress posits a distal-proximal model of stress in which a person identifies with and makes proximal, distal social attitudes that can have negative effects on their psychological well-being (Meyer, 2003). Thus, stigmatized attitudes and behaviors not only have the potential to contribute to violence or discriminatory behavior but also have a direct impact on the psychological health of the target individual. Thus, the question of how to change negative attitudes and behaviors toward TG individuals is paramount.
Researchers have sought to develop interventions aimed at reducing stigma with three basic strategies identified: protest, education and contact (Corrigan & Penn, 1999). However, to date only two such strategies have garnered empirical support: contact and education. In relation to mental illness, education strategies have received limited support (Holmes et al., 1999; see Luty et al., 2007 for an exception). In contrast, contact-based interventions yield the most dramatic changes in attitudes and behaviors; contact involving media depictions have also been demonstrated to yield positive attitude change. Comparing traditional diagnosis-centered teaching about mental illness to a humanizing approach that required students to write a first-person narrative about suffering from a mental illness, Mann and Himelein (2008) found that attitudes changed only when students were required to adopt the perspective of a mentally ill individual. In their recent meta-analysis, Pettigrew and Tropp (2006) demonstrated that contact reduces prejudice and is particularly effective when it occurs under favorable conditions (e.g., conditions of equality, cooperation, and institutional support). While a wealth of research has supported the contact hypothesis related to changing negative attitudes toward ethnic minorities, the mentally ill, the homeless, gays/lesbians and other stigmatized groups, there have been a limited number of studies evaluating associations between contact and attitudes toward the TG community (Harvey, 2002; Hill & Willoughby, 2005) and no controlled studies to evaluate the efficacy of such methods.
The current study extends work evaluating anti-stigma interventions to the TG community and seeks to evaluate whether attitude change will differ between participants receiving basic education about the transgender community and those who are educated about TG through media depictions of TG families and are asked to engage in a perspective-taking task. We hypothesize that participants in the humanizing condition who view a documentary and write a first-person narrative of transgender experiences will show a more significant change in transphobia, genderist attitudes and desire for social distance across time relative to participants in the education-only condition signaling less stigmatized and prejudicial attitudes at post-test.
Hodson (2011) recently examined the existing contact literature and found that, consistent with Pettigrew’s (1998) focus on individual differences, intergroup contact was effective (and perhaps even more effective) among individuals who were intolerant and cognitively rigid. Religious fundamentalism has been associated with anti-homosexual sentiment (Fulton et al., 1999). Whether religiosity is similarly associated with negative attitudes toward TG individuals will be explored. Whether religiosity and prior contact with the LGBTQ community will moderate intervention outcomes will also be explored
Results on the nucleon spin structure
SMC performed an investigation of the spin structure of the nucleon by
measuring deep inelastic scattering of polarised muons off polarised protons
and deuterons. A summary of the results for spin structure functions and sum
rules is given.Comment: 8 pages, LaTeX, Talk given at the Workshop on "Symmetry and Spin -
PRAHA98", Prag, September 1998. Proceedings to be published by Czech. Journ.
Phy
High-velocity hot CO emission close to Sgr A*: Herschel/HIFI submillimeter spectral survey toward Sgr A*
The properties of molecular gas, the fuel that forms stars, inside the cavity
of the circumnuclear disk (CND) are not well constrained. We present results of
a velocity-resolved submillimeter scan (~480 to 1250 GHz}) and [CII]158um line
observations carried out with Herschel/HIFI toward Sgr A*; these results are
complemented by a ~2'x2' CO (J=3-2) map taken with the IRAM 30 m telescope at
~7'' resolution. We report the presence of high positive-velocity emission (up
to about +300 km/s) detected in the wings of CO J=5-4 to 10-9 lines. This wing
component is also seen in H2O (1_{1,0}-1_{0,1}) a tracer of hot molecular gas;
in [CII]158um, an unambiguous tracer of UV radiation; but not in [CI]492,806
GHz. This first measurement of the high-velocity CO rotational ladder toward
Sgr A* adds more evidence that hot molecular gas exists inside the cavity of
the CND, relatively close to the supermassive black hole (< 1 pc). Observed by
ALMA, this velocity range appears as a collection of CO (J=3-2) cloudlets lying
in a very harsh environment that is pervaded by intense UV radiation fields,
shocks, and affected by strong gravitational shears. We constrain the physical
conditions of the high positive-velocity CO gas component by comparing with
non-LTE excitation and radiative transfer models. We infer T_k~400 K to 2000 K
for n_H~(0.2-1.0)x10^5 cm^-3. These results point toward the important role of
stellar UV radiation, but we show that radiative heating alone cannot explain
the excitation of this ~10-60 M_Sun component of hot molecular gas inside the
central cavity. Instead, strongly irradiated shocks are promising candidates.Comment: Accepted for publication in A&A Letters ( this v2 includes
corrections by language editor
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