747 research outputs found
Disordered, stretched, and semiflexible biopolymers in two dimensions
We study the effects of intrinsic sequence-dependent curvature for a two
dimensional semiflexible biopolymer with short-range correlation in intrinsic
curvatures. We show exactly that when not subjected to any external force, such
a system is equivalent to a system with a well-defined intrinsic curvature and
a proper renormalized persistence length. We find the exact expression for the
distribution function of the equivalent system. However, we show that such an
equivalent system does not always exist for the polymer subjected to an
external force. We find that under an external force, the effect of
sequence-disorder depends upon the averaging order, the degree of disorder, and
the experimental conditions, such as the boundary conditions. Furthermore, a
short to moderate length biopolymer may be much softer or has a smaller
apparent persistent length than what would be expected from the "equivalent
system". Moreover, under a strong stretching force and for a long biopolymer,
the sequence-disorder is immaterial for elasticity. Finally, the effect of
sequence-disorder may depend upon the quantity considered
Post-Prior discrepancies in CDW-EIS calculations for ion impact ionization fully differential cross sections
In this work we present fully differential cross sections (FDCSs)
calculations using post and prior version of CDW--EIS theory for helium single
ionization by 100 MeV C amu and 3.6 MeV amu Au and
Au ions. We performed our calculations for different momentum transfer
and ejected electron energies. The influence of internuclear potential on the
ejected electron spectra is taken into account in all cases. We compare our
calculations with absolute experimental measurements. It is shown that prior
version calculations give better agreement with experiments in almost all
studied cases.Comment: 9 pages, 7 figure
HIV infection is an independent risk factor for decreased 6-minute walk test distance.
BackgroundAmbulatory function predicts morbidity and mortality and may be influenced by cardiopulmonary dysfunction. Persons living with HIV (PLWH) suffer from a high prevalence of cardiac and pulmonary comorbidities that may contribute to higher risk of ambulatory dysfunction as measured by 6-minute walk test distance (6-MWD). We investigated the effect of HIV on 6-MWD.MethodsPLWH and HIV-uninfected individuals were enrolled from 2 clinical centers and completed a 6-MWD, spirometry, diffusing capacity for carbon monoxide (DLCO) and St. George's Respiratory Questionnaire (SGRQ). Results of 6-MWD were compared between PLWH and uninfected individuals after adjusting for confounders. Multivariable linear regression analysis was used to determine predictors of 6-MWD.ResultsMean 6-MWD in PLWH was 431 meters versus 462 in 130 HIV-uninfected individuals (p = 0.0001). Older age, lower forced expiratory volume (FEV1)% or lower forced vital capacity (FVC)%, and smoking were significant predictors of decreased 6-MWD in PLWH, but not HIV-uninfected individuals. Lower DLCO% and higher SGRQ were associated with lower 6-MWD in both groups. In a combined model, HIV status remained an independent predictor of decreased 6-MWD (Mean difference = -19.9 meters, p = 0.005).ConclusionsHIV infection was associated with decreased ambulatory function. Airflow limitation and impaired diffusion capacity can partially explain this effect. Subjective assessments of respiratory symptoms may identify individuals at risk for impaired physical function who may benefit from early intervention
Symmetric eikonal model for projectile-electron excitation and loss in relativistic ion-atom collisions
At impact energies GeV/u the projectile-electron
excitation and loss occurring in collisions between highly charged ions and
neutral atoms is already strongly influenced by the presence of atomic
electrons. In order to treat these processes in collisions with heavy atoms we
generalize the symmetric eikonal model, used earlier for considerations of
electron transitions in ion-atom collisions within the scope of a three-body
Coulomb problem. We show that at asymptotically high collision energies this
model leads to an exact transition amplitude and is very well suited to
describe the projectile-electron excitation and loss at energies above a few
GeV/u. In particular, by considering a number of examples we demonstrate
advantages of this model over the first Born approximation at impact energies
--30 GeV/u, which are of special interest for atomic physics
experiments at the future GSI facilities.Comment: 14 pages, 5 figure
Participatory Militias: An Analysis of an Armed Movement's Online Audience
Armed groups of civilians known as "self-defense forces" have ousted the
powerful Knights Templar drug cartel from several towns in Michoacan. This
militia uprising has unfolded on social media, particularly in the "VXM"
("Valor por Michoacan," Spanish for "Courage for Michoacan") Facebook page,
gathering more than 170,000 fans. Previous work on the Drug War has documented
the use of social media for real-time reports of violent clashes. However, VXM
goes one step further by taking on a pro-militia propagandist role, engaging in
two-way communication with its audience. This paper presents a descriptive
analysis of VXM and its audience. We examined nine months of posts, from VXM's
inception until May 2014, totaling 6,000 posts by VXM administrators and more
than 108,000 comments from its audience. We describe the main conversation
themes, post frequency and relationships with offline events and public
figures. We also characterize the behavior of VXM's most active audience
members. Our work illustrates VXM's online mobilization strategies, and how its
audience takes part in defining the narrative of this armed conflict. We
conclude by discussing possible applications of our findings for the design of
future communication technologies.Comment: Participatory Militias: An Analysis of an Armed Movement's Online
Audience. Saiph Savage, Andres Monroy-Hernandez. CSCW: ACM Conference on
Computer-Supported Cooperative Work 201
Field dependence of the temperature at the peak of the ZFC magnetization
The effect of an applied magnetic field on the temperature at the maximum of
the ZFC magnetization, , is studied using the recently obtained
analytic results of Coffey et al. (Phys. Rev. Lett. {\bf 80}(1998) 5655) for
the prefactor of the N\'{e}el relaxation time which allow one to precisely
calculate the prefactor in the N\'{e}el-Brown model and thus the blocking
temperature as a function of the coefficients of the Taylor series expansion of
the magnetocrystalline anisotropy. The present calculations indicate that even
a precise determination of the prefactor in the N\'{e}el-Brown theory, which
always predicts a monotonic decrease of the relaxation time with increasing
field, is insufficient to explain the effect of an applied magnetic field on
the temperature at the maximum of the ZFC magnetization. On the other hand, we
find that the non linear field-dependence of the magnetization along with the
magnetocrystalline anisotropy appears to be of crucial importance to the
existence of this maximum.Comment: 14 LaTex209 pages, 6 EPS figures. To appear in J. Phys.: Condensed
Matte
Thermally activated escape rates of uniaxial spin systems with transverse field
Classical escape rates of uniaxial spin systems are characterized by a
prefactor differing from and much smaller than that of the particle problem,
since the maximum of the spin energy is attained everywhere on the line of
constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is
applied, a saddle point of the energy is formed, and high, moderate, and low
damping regimes (similar to those for particles) appear. Here we present the
first analytical and numerical study of crossovers between the uniaxial and
other regimes for spin systems. It is shown that there is one HD-Uniaxial
crossover, whereas at low damping the uniaxial and LD regimes are separated by
two crossovers.Comment: 4 PR pages, 3 figures, final published versio
Landau-Zener-Stueckelberg effect in a model of interacting tunneling systems
The Landau-Zener-Stueckelberg (LZS) effect in a model system of interacting
tunneling particles is studied numerically and analytically. Each of N
tunneling particles interacts with each of the others with the same coupling J.
This problem maps onto that of the LZS effect for a large spin S=N/2. The
mean-field limit N=>\infty corresponds to the classical limit S=>\infty for the
effective spin. It is shown that the ferromagnetic coupling J>0 tends to
suppress the LZS transitions. For N=>\infty there is a critical value of J
above which the staying probability P does not go to zero in the slow sweep
limit, unlike the standard LZS effect. In the same limit for J>0 LZS
transitions are boosted and P=0 for a set of finite values of the sweep rate.
Various limiting cases such as strong and weak interaction, slow and fast sweep
are considered analytically. It is shown that the mean-field approach works
well for arbitrary N if the interaction J is weak.Comment: 13 PR pages, 15 Fig
The Impact of HAART on the Respiratory Complications of HIV Infection: Longitudinal Trends in the MACS and WIHS Cohorts
Objective: To review the incidence of respiratory conditions and their effect on mortality in HIV-infected and uninfected individuals prior to and during the era of highly active antiretroviral therapy (HAART). Design: Two large observational cohorts of HIV-infected and HIV-uninfected men (Multicenter AIDS Cohort Study [MACS]) and women (Women's Interagency HIV Study [WIHS]), followed since 1984 and 1994, respectively. Methods: Adjusted odds or hazards ratios for incident respiratory infections or non-infectious respiratory diagnoses, respectively, in HIV-infected compared to HIV-uninfected individuals in both the pre-HAART (MACS only) and HAART eras; and adjusted Cox proportional hazard ratios for mortality in HIV-infected persons with lung disease during the HAART era. Results: Compared to HIV-uninfected participants, HIV-infected individuals had more incident respiratory infections both pre-HAART (MACS, odds ratio [adjusted-OR], 2.4; 95% confidence interval [CI], 2.2-2.7; p<0.001) and after HAART availability (MACS, adjusted-OR, 1.5; 95%CI 1.3-1.7; p<0.001; WIHS adjusted-OR, 2.2; 95%CI 1.8-2.7; p<0.001). Chronic obstructive pulmonary disease was more common in MACS HIV-infected vs. HIV-uninfected participants pre-HAART (hazard ratio [adjusted-HR] 2.9; 95%CI, 1.02-8.4; p = 0.046). After HAART availability, non-infectious lung diseases were not significantly more common in HIV-infected participants in either MACS or WIHS participants. HIV-infected participants in the HAART era with respiratory infections had an increased risk of death compared to those without infections (MACS adjusted-HR, 1.5; 95%CI, 1.3-1.7; p<0.001; WIHS adjusted-HR, 1.9; 95%CI, 1.5-2.4; p<0.001). Conclusion: HIV infection remained a significant risk for infectious respiratory diseases after the introduction of HAART, and infectious respiratory diseases were associated with an increased risk of mortality. © 2013 Gingo et al
Epidemiological study of E. coli O157:H7 isolated in Northern Ireland using pulsed-field gel electrophoresis (PFGE)
In Northern Ireland over the last 7 years, there is a mean of 41.9 laboratory reports per annum of human gastrointestinal infection (range 19-54) caused by Escherichia coli O157:H7. In the preceding years 1992-1996, reports were 5.4 per annum, whereas in 1997-2000, reports increased from 30 to 54 per annum. This high level has continued on an annual basis to date. The aim of this study was therefore to retrospectively examine this period of exponential increase in reports to help ascertain the genetic relatedness of strains employing pulsed-field gel electrophoresis (PFGE), as no data on the molecular epidemiology of E. coli O157:H7 in Northern Ireland has yet been published. Clinical isolates (n=84) were PFGE typed employing Xba I digestion and resulting band profiles demonstrated the presence of 13, 9 and 16 clonal types, for 1997, 1998 and 1999, respectively. In 1998, five clonal types remained from 1997 with the introduction of 4 new clonal types, whereas in 1999, 10 new clonal types were observed, accounting for over half (58%) of the E. coli O157 isolates for that year. These data suggest that, unlike gastrointestinal infections due to thermophilic campylobacters, there was considerable genetic evolution of PFGE clonal types of E. coli O157, through the displacement and emergence of genotypes. Further studies are now required to find the environmental reservoirs of these common clonal types of clinical E. coli O157:H7 in Northern Ireland to help define sources and routes of transmission of this infection locally
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