bluuebunny/crossref_metadata_2025 huggingface dataset:
Mid-level providers demonstrate proficiency in FAST after directed training
Authors: Davis Virgil W. , Wallace J. Michael , Ahern Matthew T. , Dawson Matthew S. , Battaglia Deborah F. , Sherwood Kelly L. , Sugerman Steve A. , Mallin Michael P. , Madsen Troy E.
Published: April 2011

Introduction

Focused Assessment with Sonography for Trauma (FAST) is commonly used to detect intra-peritoneal blood as part of the evaluation of trauma patients. In our level 1 trauma center, mid-level providers (MLPs) perform serial FAST exams on trauma patients. We describe our training approach and proficiency achieved.

Methods

Subjects were MLPs with no previous training in FAST. The training consisted of hands-on training on live models, two on-line ultrasound (US) modules, and a video image review session. Participants were evaluated with pre-, post-, and 6-month follow-up video tests. Subsequently, they independently performed FAST exams which were reviewed by ED US faculty.

Results

11 MLPs participated, completing an average of 17 scans; 91% were technically adequate. Average scores were: pre-test 50.5% (31.7–68.3%), post-test 76.7% (65.9–87.8%), and 6-month test 77% (58.5–87.8%), for an initial improvement of 26.2% (p < 0.001) and a sustained improvement over the pre-test of 26.5% (p = 0.011) at 6 months.

Conclusion

MLPs demonstrated proficiency in FAST after brief training.
Epigenetic regulation of mucin genes in human cancers
Authors: Yamada Norishige , Kitamoto Sho , Yokoyama Seiya , Hamada Tomofumi , Goto Masamichi , Tsutsumida Hideaki , Higashi Michiyo , Yonezawa Suguru
Published: April 2011

Mucins are high molecular weight glycoproteins that play important roles in diagnostic and prognostic prediction and in carcinogenesis and tumor invasion. Regulation of expression of mucin genes has been studied extensively, and signaling pathways, transcriptional regulators, and epigenetic modification in promoter regions have been described. Detection of the epigenetic status of cancer-related mucin genes is important for early diagnosis of cancer and for monitoring of tumor behavior and response to targeted therapy. Effects of micro-RNAs on mucin gene expression have also started to emerge. In this review, we discuss the current views on epigenetic mechanisms of regulation of mucin genes (MUC1, MUC2, MUC3A, MUC4, MUC5AC, MUC5B, MUC6, MUC16, and MUC17) and the possible clinical applications of this epigenetic information.
Degradation‐linked ubiquitin signal and proteasome are integral components of DNA double strand break repair: New perspectives for anti‐cancer therapy
Authors: Ramadan Kristijan , Meerang Mayura
Published: April 2011

Damaged DNA leads to genomic instability that causes many diseases such as cancer. Cells evolved the DNA damage response (DDR), which recognizes and efficiently repairs damaged DNA through the action of highly coordinated signalling mechanisms. Recently, a non‐degradation‐linked Lys(K)63‐ubiquitin signal emerged as a signalling pathway essential for orchestration of the DDR after DNA double strand breaks (DSBs). How the ubiquitin‐dependent proteasomal degradation system (UPS) coordinates DDR after DSBs is still poorly understood. Here, we review the evidence, suggesting the involvement of the degradation‐linked K48‐ubiquitin signal and the proteasome at the sites of DSBs. Based on this we propose the UPS as a central element in the orchestration of the DDR at the sites of DSBs. The suggested model is also discussed in the context of anti‐cancer therapy.
Perfect timing: Epigenetic regulation of the circadian clock
Authors: Ripperger Jürgen A. , Merrow Martha
Published: April 2011

In mammals, higher order chromatin structures are critical for downsizing the genome (packaging) so that the nucleus can be small. The adjustable density of chromatin also regulates gene expression, thus this post‐genetic molecular mechanism is one of the routes by which phenotype is shaped. Phenotypes that arise without a concomitant mutation of the underlying genome are termed epigenetic phenomena. Here we discuss epigenetic phenomena from histone and DNA modification as it pertains to the dynamic regulatory processes of the circadian clock. Epigenetic phenomena certainly explain some regulatory aspects of the mammalian circadian oscillator.
Intracellular and intercellular processes determine robustness of the circadian clock
Authors: Hogenesch John B. , Herzog Erik D.
Published: April 2011

Circadian clocks are present in most organisms and provide an adaptive mechanism to coordinate physiology and behavior with predictable changes in the environment. Genetic, biochemical, and cellular experiments have identified more than a dozen component genes and a signal transduction pathway that support cell‐autonomous, circadian clock function. One of the hallmarks of biological clocks is their ability to reset to relevant stimuli while ignoring most others. We review recent results showing intracellular and intercellular mechanisms that convey this robust timekeeping to a variety of circadian cell types.
Management of Pelvic Trauma
Authors: Meeson Richard , Corr Sandra
Published: April 2011

Practical relevance Cats commonly present with pelvic trauma following road traffic accidents (RTAs). A logical step-wise approach to diagnostics and subsequent management can significantly improve the prognosis in the majority of cases. This article provides a practical guide to assist decision-making and optimise management of these cats.

Clinical challenges Affected cats may have sustained trauma to several body systems and, hence, their management can be complex, requiring good clinical, diagnostic and surgical skills (often both soft tissue and orthopaedic!).

Patient group Any cat allowed access to the outdoors is potentially at risk of being involved in an RTA and sustaining pelvic trauma. Young male cats are most commonly affected.

Evidence base Many original articles and textbook chapters have been published on aspects of pelvic trauma. However, to the authors’ knowledge, this is the first comprehensive overview of the assessment and management of the feline pelvic trauma case. The review begins by discussing initial triage and neurological examination, and then focuses, in turn, on assessment and management of the ‘tail pull’ injury, the diagnosis and management of urinary tract rupture, and the approach to managing specific pelvic fractures.
AAFP and ISFM Feline-Friendly Handling Guidelines
Authors: Rodan Ilona , Sundahl Eliza , Carney Hazel , Gagnon Anne-Claire , Heath Sarah , Landsberg Gary , Seksel Kersti , Yin Sophia
Published: April 2011

Background The number of pet cats is increasing in most countries, often outnumbering pet dogs, yet cats receive less veterinary care than their canine counterparts. 1 Clients state the difficulty of getting the cat into a carrier at home, driving to the clinic, and dealing with the fearful cat at the veterinary clinic as reasons for fewer visits. 2 Educating and preparing the client and the veterinary team with regard to respectful feline handling is necessary in order to avoid stress and accomplish the goal of good health care. Without such preparation, feline stress may escalate into fear or fear-associated aggression. The resulting stress may alter results of the physical examination and laboratory tests, leading to incorrect diagnoses (eg, diabetes mellitus) and unnecessary treatments. 3 – 5 Without compassionate and respectful handling by the veterinary team, clients may feel the team lacks skills and compassion, or does not understand cats. Injury may occur to the cat, client and/or veterinary team. 6 Clients who want to avoid stress for their cat may avoid veterinary visits or choose another practice instead.

Goals The use of feline-friendly handling techniques should reduce these problems. Handling is most successful when the veterinary team adapts the approach to each individual cat and situation. The goal of these guidelines is to provide useful information for handling cats that can lead to: Reduced fear and pain for the cat. Reinforced veterinarian—client—cat bond, trust and confidence, and thus better lifelong medical care for the cat. Improved efficiency, productivity and job satisfaction for the veterinary team. Increased client compliance. Timely reporting and early detection of medical and behavioral concerns. Fewer injuries to clients and the veterinary team. Reduced anxiety for the client.
Universality in the run-up of shock waves to the surface of a star
Authors: GUNDLACH C. , LEVEQUE R. J.
Published: April 2011

We investigate the run-up of a shock wave from inside to the surface of a perfect fluid star in equilibrium and bounded by vacuum. Near the surface we approximate the fluid motion as plane-symmetric and the gravitational field as constant. We consider the ‘hot’ equation of state P = (Γ − 1)ρe and its ‘cold’ (fixed entropy, barotropic) form P = K0ρΓ (the latter does not allow for shock heating). We numerically find that the evolution of generic initial data approaches universal similarity solutions sufficiently near the surface, and we explicitly construct these similarity solutions. The two equations of state show very different behaviour because shock heating becomes the dominant effect when it is allowed. In the barotropic case, the fluid velocity behind the shock approaches a constant value, while the density behind the shock approaches a power law in space, as the shock approaches the surface. In the hot case with shock heating, the density jumps by a constant factor through the shock, while the sound speed and fluid velocity behind the shock diverge in a whiplash effect. We tabulate the similarity exponents as a function of the equation of state parameter Γ and the stratification index n∗.
THE POLITICAL ECONOMY OF MIGRATION AND REPUTATION IN KINSHASA
Authors: Trapido Joseph
Published: April 2011

This essay presents a history of themikiliste, the high-livingbon vivantwho travels to Europe and is a central figure in Kinois urban mythology. It looks in particular at the highly theatrical exchanges engaged in by themikiliste,which relate especially to music patronage and to designer clothing. I show how these exchanges have evolved over time, both shaping and being shaped by the political economy of Kinshasa. The essay shows how such aesthetic performances should not be discussed in isolation from wider political-economic considerations. Those who participate in economies of prestige must be connected to a material base, and the ruling class, with their access to the resources of the interior, have become ever more important participants in themikilisterituals of largesse. Recently, the violent contestation ofmikilisteexchange, both in Europe and in Kinshasa, indicates that such moments of largesse may be involved in reproducing political-economic relations in the Congolese capital.
What Is Political Development? A Constitutional Perspective
Authors: Thomas George
Published: April 2011

Development approaches to the study of politics, precisely because they focus on movement through time, seem uniquely positioned to illuminate the logic and experience of the polity in a manner that cannot be captured by more conventional political science methods. And yet, political development has come to be seen as whatever historical change happens to a regime, neglecting the normative nature of the polity. The result is an “a-constitutional” approach to political development. This paper argues that political science can and should examine development in normative terms and that attempts to fit political development more securely within value-free social science threaten to rob it of its promise.
Have We Abandoned a “Constitutional Perspective” on American Political Development?
Authors: Orren Karen , Skowronek Stephen
Published: April 2011

Defining terms is a serious undertaking and one bound to stir controversy. When we decided to devote a book to this task, we were under no illusion that everyone would readily sign on to our proposal. We thought, however, that it was worth calling attention to certain conceptual problems that currently beset the study of American political development (APD). We wanted to underscore the value of tractability in claims about change over time and to demonstrate the benefits of specificity in moving this venerable research tradition forward. We regret that Professor Thomas finds our proposal objectionable, but we are even more concerned that his alternative seems to do little to address the issues that prompted our effort.
Evidence for Nipah virus recrudescence and serological patterns of captive Pteropus vampyrus
Authors: SOHAYATI A. R. , HASSAN L. , SHARIFAH S. H. , LAZARUS K. , ZAINI C. M. , EPSTEIN J. H. , SHAMSYUL NAIM N. , FIELD H. E. , ARSHAD S. S. , ABDUL AZIZ J. , DASZAK P. ,   EcoHealth Alliance
Published: April 2011

This study aimed to describe the transmission dynamics, the serological and virus excretion patterns of Nipah virus (NiV) in Pteropus vampyrus bats. Bats in captivity were sampled every 7–21 days over a 1-year period. The data revealed five NiV serological patterns categorized as high and low positives, waning, decreasing and increasing, and negative in these individuals. The findings strongly suggest that NiV circulates in wild bat populations and that antibody could be maintained for long periods. The study also found that pup and juvenile bats from seropositive dams tested seropositive, indicating that maternal antibodies against NiV are transmitted passively, and in this study population may last up to 14 months. NiV was isolated from the urine of one bat, and within a few weeks, two other seronegative bats seroconverted. Based on the temporal cluster of seroconversion, we strongly believe that the NiV isolated was recrudesced and then transmitted horizontally between bats during the study period.
Age factor and implication of human papillomavirus type-specific prevalence in women with normal cervical cytology
Authors: LAI C. H. , CHAO A. , CHANG C. J. , HUANG C. C. , WANG L. C. , HSUEH S. , LIN C. T. , WU T. I. , JAO M. S. , CHOU H. H.
Published: April 2011

The prevalence and genotype distribution of human papillomavirus (HPV) infection in women with normal cervical cytology varies widely according to the population studied. Two non-overlapping population-based cohort studies of women aged ⩾30 years for the periods 2008–2009 (n=5026) and 2004–2005 (n=10 014) were analysed. The prevalence rate of HPV was 11·0% (95% CI 10·5–11·6). HPV infection was significantly associated with age, menopausal status, and inversely associated with hormone replacement therapy. There was an increasing trend of α3/α15, α5/α6, and multiple HPV infections with increasing age. The five most common types were HPV52, 18, 53, 58 and 70, while HPV16, 31, 33 ranked 21st, 25th, and 16th, respectively, in the merged cohort with normal cytology (n=14 724). HPV16, 31, and 33 were significantly associated with abnormal cytology, which could have resulted in their rarity in the total merged cohort (n=15 040).
Microscopy is Only Skin Deep
Authors: Carmichael Stephen W.
Published: April 2011

Light optical imaging techniques that don't require labels are attractive for human studies because they are not toxic nor do they perturb the system being studied. Whereas there are several methods available to provide microscopic imaging below the surface of a tissue, they each suffer from limitations, such as low spatiotemporal resolution and a limited number of molecular signatures that can be imaged. Raman spectroscopy offers label-free contrast for major chemical species in tissue, such as water, lipids, DNA, and proteins based on vibrational spectra at light optical wavelengths. However, the Raman signal is very weak, which makes it difficult to image a sample with good temporal resolution. The recent development of stimulated Raman scattering (SRS) microscopy can overcome these limitations as demonstrated by the elegant studies of Brian Saar, Christian Freudiger, Jay Reichman, Michael Stanley, Gary Holton, and Sunney Xie. Saar et al. improved the optics and electronics for the acquisition of the backscattered signal of SRS. In SRS microscopy, the sample is excited by two lasers at different frequencies. When the difference in frequency matches a molecular vibration in the sample, the intensities of the probes change in a predictable manner. These intensity changes are small, but Saar et al. developed a new method to detect them. They chopped one of the laser beams at high frequency (MHz) and detected the intensity change in the other beam, which offered superior sensitivity. The key component was a custom-made all-analog lock-in amplifier with a very short (about 100 ns) response time. The laser probe wavelengths were tuned to match a vibrational frequency of interest and raster-scanned across the sample. Frequencies were tuned to detect CH2 stretching (primarily for lipids), OH stretching (primarily water), and CH3 stretching (primarily proteins) vibrations. Imaging of water is of particular interest in studying the transport of water-soluble compounds such as drugs.
Thinking about elections and about democratic representation
Authors: LH  , GvdS  , WTE
Published: April 2011

[Political representation] is the basis of modern representative democracy. Older and less sophisticated forms, such as direct democracy, subsist marginally, even if they keep exerting a certain attraction. But representative democracy does not carry the self-evident authority it once had. Like every modern institution it is under challenge and consequently needs to be defended. In actual politics, the defence often takes the form of discussion of the merits of one system over the other and of proposals for change. The part of this defence appertaining to constitutional scholarship is not concerned primarily with proposals and changes. It is, before all, to brush up the fundamentals underlying representative democracy, on the basis of topical issues.

There are three current issues upon which we would like to draw attention. They are: equality in structuring electoral systems, the processes of electoral reform and the rise of non-majoritarian institutions versus parliamentary democracy.
The Populist Challenge to Constitutional Democracy
Authors: Pinelli Cesare
Published: April 2011

Populism and time – Democracy and representation – The open mandate and party democracy – Democracy and non-majoritarian institutions – Populist challenge as symptom of constitutional democracy's malaise
Self-Rated Quality of Life in Mild Cognitive Impairment and Alzheimer’s Disease
Authors: Berwig M. , Leicht H. , Hartwig K. , Gertz H. J.
Published: April 2011

Background: Cognitively impaired or demented patients may have difficulty performing the complex and multidimensional appraisal required by self-ratings (SR) of quality of life (QoL). Even healthy subjects often refer to their current mood state for QoL self-assessment. Therefore, it is hypothesized that patients rely on current mood state as a reference point for QoL SR, and that the degree of reliance increases with the level of cognitive impairment. Methods: Two consecutive samples of 14 patients with mild cognitive impairment (MCI) and 16 patients with Alzheimer’s disease (AD) were examined using the self-rated Dementia-Quality of Life (DEMQoL), a multidimensional mood state questionnaire (MDBF-A, Mehrdimensionaler Befindlichkeitsfragebogen), and the Mini-Mental State Examination (MMSE; MCI: mean = 25.1, SD = 2.1; AD: mean = 20.3, SD = 2.7). Results: As expected, correlations between current mood state and QoL SR (DEMQoL) were highly significant in AD patients but not in MCI patients. The degree of association for all significant correlations was also significantly higher in AD than in MCI patients. Conclusions: The results indicate that SR of QoL are more affectively distorted in AD than MCI. Mood state questionnaires may be an alternative to QoL questionnaires for AD patients, in particular if mood state ratings can be averaged across several points of assessment thus enhancing their validity.
Practicing biochemistry without a licence?
Authors: Rose Steven
Published: April 2011

The turf war between molecular biology and biochemistry about which discipline is better suited to describe life have taken a new turn with the advent of ‘omics’ – which seem to embrace the original definition of what biochemistry is about.
Each under his own vine and fig tree
Authors: Jacobs Howy
Published: April 2011

Turkey has been a member of Europe's molecular biology community for almost 20 years. Yet Europe's politicians are obstructing its ambition to join the EU, on grounds that reek of prejudice. Howy argues that it's time for the rest of Europe to follow the lead of its scientists, to mutual benefit.
Mass flow rate measurements in microtubes: From hydrodynamic to near free molecular regime
Authors: Perrier P. , Graur I. A. , Ewart T. , Méolans J. G.
Published: April 2011

An experimental investigation of the reflection/accommodation process at the wall in a single silica microtube and isothermal stationary flow conditions was carried out. Several gases and different diameters were studied through various regimes. Especially for helium, the Knudsen number range was investigated as far as the free molecular regime. This kind of investigation requires a powerful experimental platform to measure mass flow rates, which we have carried out. An analytic expression of the mass flow rate, based on the Navier–Stokes equations with second order boundary condition, was used to yield the tangential momentum accommodation coefficient (TMAC) in the 0.003–0.3 Knudsen number range. Otherwise, the experimental results of the mass flow rate were compared with theoretical values calculated from kinetic approaches using variable TMAC as parameter over the 0.3–30 Knudsen number range, and an overall agreement appears through the comparison. Finally, whatever the theoretical approach the TMAC obtained from gas (nitrogen, xenon, argon, and helium)-surface (fused silica) pairs is similar and lower than unity. A tendency of the TMAC values seems to appear according to the molecular mass of the gases. In addition for each gas, the second order slip coefficient magnitude seems to decrease when the tube diameter increases.
Pyrene: Hydrogenation, hydrogen evolution, and π-band model
Authors: Rasmussen Jakob Arendt , Henkelman Graeme , Hammer Bjørk
Published: April 2011

We present a theoretical investigation of the hydrogenation of pyrene and of the subsequent molecular hydrogen evolution. Using density functional theory (DFT) at the GGA-PBE level, the chemical binding of atomic hydrogen to pyrene is found to be exothermic by up to 1.6 eV with a strong site dependence. The edge C atoms are found most reactive. The barrier for the formation of the hydrogen–pyrene bond is small, down to 0.06 eV. A second hydrogen binds barrierless at many sites. The most stable structure of dihydrogenpyrene is more stable by 0.64 eV than pyrene plus a molecular hydrogen molecule and a large barrier of 3.7 eV for the molecular hydrogen evolution is found. Using a simple tight-binding model we demonstrate that the projected density of π-states can be used to predict the most stable binding sites for hydrogen atoms and the model is used to investigate the most favorable binding sites on more hydrogenated pyrene molecules and on coronene. Some of the DFT calculations were complemented with hybrid-DFT (PBE0) showing a general agreement between the DFT and hybrid-DFT results.
Dynamics of explosively imploded pressurized tubes
Authors: Szirti Daniel , Loiseau Jason , Higgins Andrew , Tanguay Vincent
Published: April 2011

The detonation of an explosive layer surrounding a pressurized thin-walled tube causes the formation of a virtual piston that drives a precursor shock wave ahead of the detonation, generating very high temperatures and pressures in the gas contained within the tube. Such a device can be used as the driver for a high energy density shock tube or hypervelocity gas gun. The dynamics of the precursor shock wave were investigated for different tube sizes and initial fill pressures. Shock velocity and standoff distance were found to decrease with increasing fill pressure, mainly due to radial expansion of the tube. Adding a tamper can reduce this effect, but may increase jetting. A simple analytical model based on acoustic wave interactions was developed to calculate pump tube expansion and the resulting effect on the shock velocity and standoff distance. Results from this model agree quite well with experimental data.
Lattice model of oligonucleotide hybridization in solution. I. Model and thermodynamics
Authors: Araque Juan C. , Panagiotopoulos Athanasios Z. , Robert Marc A.
Published: April 2011

A coarse-grained lattice model of DNA oligonucleotides is proposed to investigate the general mechanisms by which single-stranded oligonucleotides hybridize to their complementary strands in solution. The model, based on a high-coordination cubic lattice, is simple enough to allow the direct simulation of DNA solutions, yet capturing how the fundamental thermodynamic processes are microscopically encoded in the nucleobase sequences. Physically relevant interactions are considered explicitly, such as interchain excluded volume, anisotropic base-pairing and base-stacking, and single-stranded bending rigidity. The model is studied in detail by a specially adapted Monte Carlo simulation method, based on parallel tempering and biased trials, which is designed to overcome the entropic and enthalpic barriers associated with the sampling of hybridization events of multiple single-stranded chains in solution. This methodology addresses both the configurational complexity of bringing together two complementary strands in a favorable orientation (entropic barrier) and the energetic penalty of breaking apart multiple associated bases in a double-stranded state (enthalpic barrier). For strands with sequences restricted to nonstaggering association and homogeneous pairing and stacking energies, base-pairing is found to dominate the hybridization over the translational and conformational entropy. For strands with sequence-dependent pairing corresponding to that of DNA, the complex dependence of the model's thermal stability on concentration, sequence, and degree of complementarity is shown to be qualitatively and quantitatively consistent both with experiment and with the predictions of statistical mechanical models.
Optimized design of a low-resistance electrical conductor for the multimegahertz range
Authors: Kurs André , Kesler Morris , Johnson Steven G.
Published: April 2011

We propose a design for a conductive wire composed of several mutually insulated coaxial conducting shells. With the help of numerical optimization, it is possible to obtain electrical resistances significantly lower than those of a heavy-gauge copper wire or litz wire in the 2–20 MHz range. Moreover, much of the reduction in resistance can be achieved for just a few shells; in contrast, litz wire would need to contain ∼104 strands to perform comparably in this frequency range.
Shock compression and spallation of palladium bicrystals with a Σ5 grain boundary
Authors: Pham Hieu H. , Arman Bedri , Luo S. N. , Çağin Tahir
Published: April 2011

We investigate an elementary process of shock response of grain boundaries (GBs) using molecular dynamics simulations: shock compression and spallation in Pd bicrystals with a symmetric Σ5/(210)/〈100〉 GB. The loading direction is normal to GB. An elastic shock may induce the elastic-plastic or two-wave structure at the GB. The GB serves as a wave scattering center for the transverse motion perpendicular to the GB rotation axis and the shock direction: it induces a phase shift of 180∘, an increase in the amplitude of the particle velocity, GB sliding and grain orientation distortion. The GB is the preferred nucleation site both for dislocations and voids. Our results suggest that both microstructure and the loading geometry contribute to dynamic response of a solid.
Exchange bias in a ferromagnet/antiferromagnet system with TC≪TN
Authors: Sossmeier K. D. , Pereira L. G. , Schmidt J. E. , Geshev J.
Published: April 2011

This paper reports experimental results obtained on an unconventional exchange bias (EB) system where the ferromagnetic layer, Ni0.75Cu0.25, has lower ordering temperature (TC) than that (TN) of the antiferromagnetic one, NiO, with emphasis on modifying EB through either magnetic annealing or light-ion irradiation. Samples were cooled from temperatures higher than TN or in between TC and TN to room temperature with magnetic field applied in different in-plane directions. Upon ion irradiation, magnetic fields, parallel or antiparallel to the orientation of the field present during the films deposition, were applied to explore different effects on EB. We found that the EB direction can be completely reversed by means of either annealing or ion bombardment; however, both postdeposition treatments provide very little variation of the EB field value over that produced during the film’s growth. The importance of the annealing field strength was also discussed. The results were interpreted based on a mechanism which assumes that the interfacial moments adjacent to the antiferromagnetic layer are responsible for establishing the exchange biasing in the paramagnetic state.
Unusual ground states via monotonic convex pair potentials
Authors: Marcotte É. , Stillinger F. H. , Torquato S.
Published: April 2011

We have previously shown that inverse statistical-mechanical techniques allow the determination of optimized isotropic pair interactions that self-assemble into low-coordinated crystal configurations in the d-dimensional Euclidean space \documentclass[12pt]{minimal}\begin{document}$\mathbb {R}^d$\end{document}Rd. In some of these studies, pair interactions with multiple extrema were optimized. In the present work, we attempt to find pair potentials that might be easier to realize experimentally by requiring them to be monotonic and convex. Encoding information in monotonic convex potentials to yield low-coordinated ground-state configurations in Euclidean spaces is highly nontrivial. We adapt a linear programming method and apply it to optimize two repulsive monotonic convex pair potentials, whose classical ground states are counterintuitively the square and honeycomb crystals in \documentclass[12pt]{minimal}\begin{document}$\mathbb {R}^2$\end{document}R2. We demonstrate that our optimized pair potentials belong to two wide classes of monotonic convex potentials whose ground states are also the square and honeycomb crystal. We show that these unexpected ground states are stable over a nonzero number density range by checking their (i) phonon spectra, (ii) defect energies and (iii) self assembly by numerically annealing liquid-state configurations to their zero-temperature ground states.
Computer simulation study of the phase behavior and structural relaxation in a gel-former modeled by three-body interactions
Authors: Saw Shibu , Ellegaard Niels L. , Kob Walter , Sastry Srikanth
Published: April 2011

We report a computer simulation study of a model gel-former obtained by modifying the three-body interactions of the Stillinger–Weber potential for silicon. This modification reduces the average coordination number and consequently shifts the liquid–gas phase coexistence curve to low densities, thus facilitating the formation of gels without phase separation. At low temperatures and densities, the structure of the system is characterized by the presence of long linear chains interconnected by a small number of three coordinated junctions at random locations. At small wave vectors the static structure factor shows a nonmonotonic dependence on temperature, a behavior which is due to the competition between the percolation transition of the particles and the stiffening of the formed chains. We compare in detail the relaxation dynamics of the system as obtained from molecular dynamics with the one obtained from Monte Carlo dynamics. We find that the bond correlation function displays stretched exponential behavior at moderately low temperatures and densities, but exponential relaxation at low temperatures. The bond lifetime shows an Arrhenius behavior, independent of the microscopic dynamics. For the molecular dynamics at low temperatures, the mean squared displacement and the (coherent and incoherent) intermediate scattering function display at intermediate times a dynamics with ballistic character and we show that this leads to compressed exponential relaxation. For the Monte Carlo dynamics we always find an exponential or stretched exponential relaxation. Thus we conclude that the compressed exponential relaxation observed in experiments is due to the out-of-equilibrium dynamics.
Characterization of C4H in the A2Π and X2Σ+ states by double resonance four-wave mixing
Authors: Mazzotti Fabio J. , Raghunandan Ranjini , Esmail Aaseef Muhammed , Tulej Marek , Maier John P.
Published: April 2011

The B2Π − X2Σ+ electronic spectrum of C4H has been studied by degenerate and double resonance four-wave mixing. The technique identifies vibrational levels in the X2Σ+ ground state. Its sensitivity and unique characteristics permit detection of new levels. The A2Π state lying 222 cm−1 above the X2Σ ground state is also observed, confirming the analysis from anion photoelectron spectroscopy but with improved accuracy. Vibrational level determination in the A2Π electronic manifold up to 700 cm−1 above v = 0 is made. A Renner–Teller analysis is carried out for the two lowest bending modes v6 and v7 in the A2Π state by diagonalization of the effective Hamiltonian matrix. The Renner–Teller parameters ∈ 6, ∈ 7, and ∈ 67, the vibrations ω6 and ω7 and the spin–orbit coupling constant Aso are determined.
Validity of Saha’s equation of thermal ionization for negatively charged spherical particles in complex plasmas in thermal equilibrium
Authors: Sodha M. S. , Mishra S. K.
Published: April 2011

The authors have discussed the validity of Saha’s equation for the charging of negatively charged spherical particles in a complex plasma in thermal equilibrium, even when the tunneling of the electrons, through the potential energy barrier surrounding the particle is considered. It is seen that the validity requires the probability of tunneling of an electron through the potential energy barrier surrounding the particle to be independent of the direction (inside to outside and vice versa) or in other words the Born’s approximation should be valid.
Positron annihilation and relaxation dynamics from dielectric spectroscopy and nuclear magnetic resonance: Cis–trans-1,4-poly(butadiene)
Authors: Bartoš J. , Šauša O. , Schwartz G. A. , Alegría A. , Alberdi J. M. , Arbe A. , Krištiak J. , Colmenero J.
Published: April 2011

We report a joint analysis of positron annihilation lifetime spectroscopy (PALS), dielectric spectroscopy (BDS), and nuclear magnetic resonance (NMR) on cis–trans-1,4-poly(butadiene) (c–t-1,4-PBD). Phenomenological analysis of the orthopositronium lifetime τ3 − T dependence by linear fitting reveals four characteristic PALS temperatures: $T_{b1} ^G = {\rm 0}{\rm.63}T_g^{{\rm PALS}}$Tb1G=0.63Tg PALS , $T_g^{{\rm PALS}}$Tg PALS , $T_{b1} ^L = 1.22T_g^{{\rm PALS}},$Tb1L=1.22Tg PALS , and $T_{b2} ^L = 1.52T_g^{{\rm PALS}}$Tb2L=1.52Tg PALS . Slight bend effects in the glassy and supercooled liquid states are related to the fast or slow secondary β process, from neutron scattering, respectively, the latter being connected with the trans-isomers. In addition, the first bend effect in the supercooled liquid coincides with a deviation of the slow effective secondary βeff relaxation related to the cis-isomers from low-T Arrhenius behavior to non-Arrhenius one and correlates with the onset of the primary α process from BDS. The second plateau effect in the liquid state occurs when τ3 becomes commensurable with the structural relaxation time τα(Tb2). It is also approximately related to its crossover from non-Arrhenius to Arrhenius regime in the combined BDS and NMR data. Finally, the combined BDS and NMR structural relaxation data, when analyzed in terms of the two-order parameter (TOP) model, suggest the influence of solidlike domains on both the annihilation behavior and the local and segmental chain mobility in the supercooled liquid. All these findings indicate the influence of the dynamic heterogeneity in both the primary and secondary relaxations due to the cis–trans isomerism in c–t-1,4-PBD and their impact into the PALS response.
Giant reversible anisotropic magnetocaloric effect in an antiferromagnetic EuFe2As2 single crystal
Authors: Kim M. S. , Sung N. H. , Son Yoonkook , Ko M. S. , Cho B. K.
Published: April 2011

Here, we report the characterization of a giant reversible anisotropic magnetocaloric effect in a EuFe2As2 single crystal. The magnetic properties of EuFe2As2 single crystals are quite interesting; they display a small magnetic hysteresis, anisotropy, and a first-order magnetic phase transition. The maximum magnetic entropy change in in-plane magnetic-field direction was 14.6 J/kg K around 20 K and out-of-plane was 10.3 J/kg K around 20 K as a result of changing the magnetic field from 0 to 5 T. These results suggest the possibility of using EuFe2As2 single crystals in magnetic refrigeration applications.
Analytical ferromagnetic hysterons with various anisotropies
Authors: Petrila Iulian , Stancu Alexandru
Published: April 2011

A new critical reflection on the anisotropic constraints of the ferromagnetic particles allow us to analytically describe the behavior of complex ferromagnetic systems. The anisotropic constraints of each individual ferromagnetic particle such as magneto-crystalline, shape, interface, defects, domain wall, or other induced influences are described in a simplified manner. The first approximation of anisotropy free energy density provides an analytical description of various magnetization processes even in the case of very complex anisotropic influences. The hysteretic behavior described by this model, including both reversible and irreversible processes, is presented and discussed for the typical anisotropy cases observed in ferromagnetic materials: uniaxial, biaxial, cubic, and orthorhombic. This practical method to model hysteresis for various types of anisotropy could be fundamentally important for many studies that demand very efficient algorithms at the level of single-domain magnetic elements.
Molecular dynamics study on evaporation and condensation of n-dodecane at liquid–vapor phase equilibria
Authors: Cao Bing-Yang , Xie Jian-Fei , Sazhin Sergei S.
Published: April 2011

Molecular dynamics simulations are performed to study the evaporation and condensation of n-dodecane (C12H26) at temperatures in the range 400–600 K. A modified optimized potential for liquid simulation model is applied to take into account the Lennard-Jones, bond bending and torsion potentials with the bond length constrained. The equilibrium liquid–vapor n-dodecane interface thickness is predicted to be ∼1.2–2.0 nm. It is shown that the molecular chains lie preferentially parallel to the interface in the liquid–vapor transition region. The predicted evaporation/condensation coefficient decreased from 0.9 to 0.3 when temperature increased from 400 to 600 K. These values can be used for the formulation of boundary conditions in the kinetic modeling of droplet heating and evaporation processes; they are noticeably different from those predicted by the transition state theory. We also present the typical molecular behaviors in the evaporation and condensation processes. The molecular exchange in condensation, typical for simple molecules, has never been observed for n-dodecane molecular chains.
Bell-polynomial approach and N-soliton solution for the extended Lotka–Volterra equation in plasmas
Authors: Qin Bo , Tian Bo , Liu Li-Cai , Wang Ming , Lin Zhi-Qiang , Liu Wen-Jun
Published: April 2011

Symbolically investigated in this paper is the extended Lotka–Volterra (ELV) equation, which can govern the kinetics of the discrete peaks of the weak Langmuir turbulence in plasmas without the linear damping and random noise. Binary Bell polynomials are applied to the bilinearization of the discrete system. Bilinear Bäcklund transformation of the ELV equation is constructed. N-soliton solution in terms of the extended Casorati determinant is also presented and verified. Propagation and interaction behaviors of the Langmuir turbulence are analyzed. It is demonstrated that the number of the interacting Langmuir waves can influence the soliton velocity and amplitude as well as the collision phase shift. Graphic illustrations of the solitonic collisions show that the repulsion effects and nonlinear interactions are also associated with the number of the interacting Langmuir waves.
The Weyl group of the fine grading of $sl(n,\mathbb {C})$sl(n,C) associated with tensor product of generalized Pauli matrices
Authors: Han Gang
Published: April 2011

We consider the fine grading of \documentclass[12pt]{minimal}\begin{document}$sl(n,\mathbb C)$\end{document}sl(n,C) induced by tensor product of generalized Pauli matrices in the paper. Regard \documentclass[12pt]{minimal}\begin{document}$PGL(n,\mathbb C)$\end{document}PGL(n,C) as the inner automorphism group of \documentclass[12pt]{minimal}\begin{document}$sl(n,\mathbb C)$\end{document}sl(n,C). Based on the classification of maximal abelian subgroups of \documentclass[12pt]{minimal}\begin{document}$PGL(n,\mathbb C)$\end{document}PGL(n,C) consisting of diagonalizable automorphisms by Havlicek et al., we prove that any such subgroup K of \documentclass[12pt]{minimal}\begin{document}$PGL(n,\mathbb C)$\end{document}PGL(n,C) is a symplectic abelian group and its Weyl group, which describes the symmetry of the fine grading induced by the action of K, is just the isometry group of the symplectic abelian group K. For a finite symplectic abelian group, it is also proved that its isometry group is always generated by the transvections contained in it.
Structural phase transitions of barium halide nanocrystals in fluorozirconate glasses studied by Raman spectroscopy
Authors: Pfau C. , Bohley C. , Miclea P.-T. , Schweizer S.
Published: April 2011

Rare-earth-doped fluorochlorozirconate (FCZ) and fluorobromozirconate (FBZ) glasses developed for fluorescence applications are analyzed, with particular attention paid to their phonon energy spectra. After thermal processing of as-made Eu-doped FCZ and FBZ glasses, Raman measurements show additional phonon bands at low phonon energies, indicating the formation of BaCl2 and BaBr2 nanocrystals, respectively. The phonon bands can be assigned to hexagonal, orthorhombic, or a mixture of both phases of BaCl2 and BaBr2 depending on the annealing conditions. Apart from line broadening, the Raman spectra of the orthorhombic nanocrystals agree well with those of BaCl2 and BaBr2 bulk crystals, while the metastable hexagonal phases of BaCl2 and BaBr2 are investigated only in appropriately treated FCZ and FBZ glasses, respectively. The experimental Raman spectra are compared to first principle studies of the phonon frequencies of the hexagonal and orthorhombic phases of both barium halides, showing good agreement.
The photodissociation dynamics of tetrachloroethylene
Authors: Herath Nuradhika , Hause Michael L. , Suits Arthur G.
Published: April 2011

We present a direct current slice imaging study of tetrachloroethylene (C2Cl4) photodissociation, probing the resulting ground state Cl (2P3/2) and spin-orbit excited state Cl* (2P1/2) products. We report photofragment images, total translational energy distributions and the product branching ratio of Cl*/Cl following dissociation at 235 and 202 nm, obtained using a two-color reduced-Doppler dissociation/probe. Near 235 nm, the Cl translational energy distribution shows a peak at the limit of the available energy, indicating a direct dissociation through a σ*(C–Cl) ← π (C=C) transition, which is superimposed on a broader underlying distribution. The ground state Cl image and associated translational energy distribution at 202 nm is broad and peaked at lower energy, suggesting either internal conversion to the ground state or a lower excited state prior to dissociation. The Cl* images are similarly broad at both wavelengths. The branching ratio is presented as a function of recoil energy, but after integration shows a near-statistical average of Cl:Cl* as 70:30 at both wavelengths. All the images are largely isotropic, with anisotropy parameters (β) of 0.05 ± 0.03.
A comparison of implicit- and explicit-solvent simulations of self-assembly in block copolymer and solute systems
Authors: Spaeth Justin R. , Kevrekidis Ioannis G. , Panagiotopoulos Athanassios Z.
Published: April 2011

We have developed explicit- and implicit-solvent models for the flash nanoprecipitation process, which involves rapid coprecipitation of block copolymers and solutes by changing solvent quality. The explicit-solvent model uses the dissipative particle dynamics (DPD) method and the implicit-solvent model uses the Brownian dynamics (BD) method. Each of the two models was parameterized to match key properties of the diblock copolymer (specifically, critical micelle concentration, diffusion coefficient, polystyrene melt density, and polyethylene glycol radius of gyration) and the hydrophobic solute (aqueous solubility, diffusion coefficient, and solid density). The models were simulated in the limit of instantaneous mixing of solvent with antisolvent. Despite the significant differences in the potentials employed in the implicit- and explicit-solvent models, the polymer-stabilized nanoparticles formed in both sets of simulations are similar in size and structure; however, the dynamic evolution of the two simulations is quite different. Nanoparticles in the BD simulations have diffusion coefficients that follow Rouse behavior (D ∝ M−1), whereas those in the DPD simulations have diffusion coefficients that are close to the values predicted by the Stokes–Einstein relation (D ∝ R−1). As the nanoparticles become larger, the discrepancy between diffusion coefficients grows. As a consequence, BD simulations produce increasingly slower aggregation dynamics with respect to real time and result in an unphysical evolution of the nanoparticle size distribution. Surface area per polymer of the stable explicit-solvent nanoparticles agrees well with experimental values, whereas the implicit-solvent nanoparticles are stable when the surface area per particle is roughly two to four times larger. We conclude that implicit-solvent models may produce questionable results when simulating nonequilibrium processes in which hydrodynamics play a critical role.
MO.Fe2O3 nanoparticles for self-controlled magnetic hyperthermia
Authors: Apostolov A. T. , Apostolova I. N. , Wesselinowa J. M.
Published: April 2011

Using a model Hamiltonian and the Green’s function technique for the Zn doped Mn-ferrite, Mn1-xZnxO.Fe2O3, and the Gd doped Zn-ferrite, ZnGdxFe(2-x)O4, nanoparticles of different compositions x were studied. The phase transition temperature, TC, and the coercive field, Hc, for different samples dependent upon composition, particle size, and shape were investigated. An attempt was made to enhance or to lower the TC of the nanoparticles to the optimum temperature required in magnetic hyperthermia (42–43°C).