321 research outputs found
Hydrodynamic singularities and clustering in a freely cooling inelastic gas
We employ hydrodynamic equations to follow the clustering instability of a
freely cooling dilute gas of inelastically colliding spheres into a
well-developed nonlinear regime. We simplify the problem by dealing with a
one-dimensional coarse-grained flow. We observe that at a late stage of the
instability the shear stress becomes negligibly small, and the gas flows solely
by inertia. As a result the flow formally develops a finite time singularity,
as the velocity gradient and the gas density diverge at some location. We argue
that flow by inertia represents a generic intermediate asymptotic of unstable
free cooling of dilute inelastic gases.Comment: 4 pages, 4 figure
Testing the influence of acceleration on time dilation using a rotating M\"Ossbauer absorber
The aim of the experiment series was to test the influence of acceleration on
time dilation by measuring the relative spectral shift between the resonance
spectra of a rotating Mossbauer absorber with acceleration anti-parallel and
parallel to the direction of the incident beam. Based on the experiences and
know-how acquired in our previous experiments, We collected data for rotation
frequencies up to 510Hz in both directions of rotation and also used different
slits. For each run with high rotation, we observed a stable statistically
significant relative shift between the spectra of the two states with opposite
acceleration. This indicates the influence of acceleration on time dilation.
However, we found that this shift also depends on the choice of the slit, and
on the direction of rotation. These new unexpected findings, resulting from the
loss of symmetry in obtaining the resonant lines in the two states, could
overshadow the relative shift due to acceleration. This loss of the symmetry is
caused by the deflection of the radiative decay due to the Nuclear Lighthouse
effect from the rotating Mossbauer absorber. We also found that it is
impossible to keep the alignment (between the optical and the dynamical rotor
systems) with accuracy needed for such experiment, for long runs, which
resulted in the reduction of the accuracy of the observed relative shift. These
prevent us to claim with certainty the influence of acceleration on time
dilation using the currently available technology. An improved KB optics with
focal spot of less than 1 micron to avoid the use of a slit and a more rigid
mounting of the rotor system, are necessary for the success of such experiment.
Hopefully, these findings together with the indispensable plan for a conclusive
experiment presented in the paper, will prove useful to future experimentalists
wishing to pursue such an experiment
Brain perfusion imaging with voxel-based analysis in secondary progressive multiple sclerosis patients with a moderate to severe stage of disease: a boon for the workforce
Background: The present study was carried out to evaluate cerebral perfusion in multiple sclerosis (MS) patients
with a moderate to severe stage of disease. Some patients underwent hyperbaric oxygen therapy (HBOT) and brain
perfusion between before and after that was compared.
Methods: We retrospectively reviewed 25 secondary progressive (SP)-MS patients from the hospital database.
Neurological disability evaluated by Expanded Disability Status Scale Score (EDSS). Brain perfusion was performed
by (99 m) Tc-labeled bicisate (ECD) brain SPECT and the data were compared using statistical parametric mapping
(SPM). In total, 16 patients underwent HBOT. Before HBOT and at the end of 20 sessions of oxygen treatment,
99mTc-ECD brain perfusion single photon emission computed tomography (SPECT) was performed again then
the results were evaluated and compared. Brain perfusion was performed by (99 m) Tc-labeled bicisate (ECD) brain
SPECT and the data were compared using statistical parametric mapping (SPM).
Results: A total of 25 SP-MS patients, 14 females (56 %) and 11 males (44 %) with a mean age of 38.92 ± 11.
28 years included in the study. The mean disease duration was 8.70 ± 5.30 years. Of the 25 patients, 2 (8 %) had
a normal SPECT and 23 (92 %) had abnormal brain perfusion SPECT studies. The study showed a significant
association between severity of perfusion impairment with disease duration and also with EDSS (P <0.05). There
was a significant improvement in pre- and post-treatment perfusion scans (P <0.05), but this did not demonstrate
a significant improvement in the clinical subjective and objective evaluation of patients (P >0.05).
Conclusions: This study depicted decreased cerebral perfusion in SP-MS patients with a moderate to severe
disability score and its association with clinical parameters. Because of its accessibility, rather low price, practical
ease, and being objective quantitative information, brain perfusion SPECT can be complementing to other
diagnostic modalities such as MRI and clinical examinations in disease surveillance and monitoring. The literature
on this important issue is extremely scarce, and follow up studies are required to assess these preliminary results
Pathophysiology of Crohn’s disease inflammation and recurrence
Chron's Disease is a chronic inflammatory intestinal disease, first described at the beginning of the last century. The disease is characterized by the alternation of periods of flares and remissions influenced by a complex pathogenesis in which inflammation plays a key role. Crohn's disease evolution is mediated by a complex alteration of the inflammatory response which is characterized by alterations of the innate immunity of the intestinal mucosa barrier together with a remodeling of the extracellular matrix through the expression of metalloproteins and increased adhesion molecules expression, such as MAcCAM-1. This reshaped microenvironment enhances leucocytes migration in the sites of inflammation, promoting a TH1 response, through the production of cytokines such as IL-12 and TNF-α. IL-12 itself and IL-23 have been targeted for the medical treatment of CD. Giving the limited success of medical therapies, the treatment of the disease is invariably surgical. This review will highlight the role of inflammation in CD and describe the surgical approaches for the prevention of the almost inevitable recurrence
The smectic order of wrinkles
A thin elastic sheet lying on a soft substrate develops wrinkled patterns when subject to an external forcing or as a result of geometric incompatibility. Thin sheet elasticity and substrate response equip such wrinkles with a global preferred wrinkle spacing length and with resistance to wrinkle curvature. These features are responsible for the liquid crystalline smectic-like behaviour of such systems at intermediate length scales. This insight allows better understanding of the wrinkling patterns seen in such systems, with which we explain pattern breaking into domains, the properties of domain walls and wrinkle undulation. We compare our predictions with numerical simulations and with experimental observations
Sexual violence in Iraq: Challenges for transnational feminist politics
The article discusses sexual violence by ISIS against women in Iraq, particularly Yezidi women, against the historical background of broader sexual and gender-based violence. It intervenes in feminist debates about how to approach and analyse sexual and wider gender-based violence in Iraq specifically and the Middle East more generally. Recognizing the significance of positionality, the article argues against dichotomous positions and for the need to look at both macrostructural configurations of power pertaining to imperialism, neoliberalism and globalization on the one hand, and localized
expressions of patriarchy, religious interpretations and practices and cultural norms on the other hand. Finally, the article reflects on the question of what a transnational feminist solidarity might look like in relation to sexual violence by ISIS
HIVAN and medication use in chronic dialysis patients in the United States: analysis of the USRDS DMMS Wave 2 study
BACKGROUND: The use and possible effects of factors known to improve outcomes in patients with human immunodeficiency virus associated nephropathy (HIVAN), namely of angiotensin converting enzyme inhibitors (ACE) and antiretroviral therapy, has not been reported for a national sample of dialysis patients. METHODS: We conducted a historical cohort study of the United States Renal Data System (USRDS) Dialysis Morbidity and Mortality Study (DMMS) Wave 2 to identify risk factors associated with increased mortality in these patients. Data were available for 3374 patients who started dialysis and were followed until March 2000. Cox Regression analysis was used to model adjusted hazard ratios (AHR) with HIVAN as a cause of end stage renal disease (ESRD) and its impact on mortality during the study period, adjusted for potential confounders. RESULTS: Of the 3374 patients who started dialysis, 36 (1.1%) had ESRD as a result of HIVAN. Only 22 (61%) of patients with HIVAN received antiretroviral agents, and only nine patients (25%) received combination antiretroviral therapy, and only 14% received ACE inhibitors. Neither the use of multiple antiretroviral drugs (AHR, 0.62, 95% CI, 0.10, 3.86, p = 0.60), or ACE inhibitors were associated with a survival advantage. Patients with HIVAN had an increased risk of mortality (adjusted hazard ratio, 4.74, 95% Confidence Interval, 3.12, 7.32, p < 0.01) compared to patients with other causes of ESRD. CONCLUSIONS: Medications known to improve outcomes in HIV infected patients were underutilized in patients with HIVAN. Adjusted for other factors, a primary diagnosis of HIVAN was associated with increased mortality compared with other causes of ESRD
The Universal One-Loop Effective Action
We present the universal one-loop effective action for all operators of
dimension up to six obtained by integrating out massive, non-degenerate
multiplets. Our general expression may be applied to loops of heavy fermions or
bosons, and has been checked against partial results available in the
literature. The broad applicability of this approach simplifies one-loop
matching from an ultraviolet model to a lower-energy effective field theory
(EFT), a procedure which is now reduced to the evaluation of a combination of
matrices in our universal expression, without any loop integrals to evaluate.
We illustrate the relationship of our results to the Standard Model (SM) EFT,
using as an example the supersymmetric stop and sbottom squark Lagrangian and
extracting from our universal expression the Wilson coefficients of
dimension-six operators composed of SM fields.Comment: 30 pages, v2 contains additional comments and corrects typos, version
accepted for publication in JHE
Foldable structures made of hydrogel bilayers
We discuss self-folding of a thin sheet by using patterned hydrogel bilayers, which act as hinges connecting flat faces. Folding is actuated by heterogeneous swelling due to different crosslinking densities of the polymer network in the two layers. Our analysis is based on a dimensionally reduced plate model, obtained by applying a recently developed theory [1], which provides us with an explicit connection between (three-dimensional) material properties and the curvatures induced at the hinges. This connection offers a recipe for the fabrication and design of the bilayers, by providing the values of the cross-linking density of each layer that need to be imprinted during polymerization in order to produce a desired folded shape upon swelling
Interpreting a 750 GeV diphoton resonance
We discuss the implications of the significant excesses in the diphoton final
state observed by the LHC experiments ATLAS and CMS around a diphoton invariant
mass of 750 GeV. The interpretation of the excess as a spin-zero s-channel resonance implies
model-independent lower bounds on both its branching ratio and its coupling to photons,
which stringently constrain dynamical models. We consider both the case where the
excess is described by a narrow and a broad resonance. We also obtain model-independent
constraints on the allowed couplings and branching fractions to final states other than
diphotons, by including the interplay with 8 TeV searches. These results can guide attempts
to construct viable dynamical models of the resonance. Turning to specific models,
our findings suggest that the anomaly cannot be accounted for by the presence of only an
additional singlet or doublet spin-zero field and the Standard Model degrees of freedom; this
includes all two-Higgs-doublet models. Likewise, heavy scalars in the MSSM cannot explain
the excess if stability of the electroweak vacuum is required, at least in a leading-order analysis.
If we assume that the resonance is broad we find that it is challenging to find a weakly
coupled explanation. However, we provide an existence proof in the form of a model with
vectorlike quarks with large electric charge that is perturbative up to the 100 TeV scale.
For the narrow-resonance case a similar model can be perturbative up to high scales also
with smaller charges. We also find that, in their simplest form, dilaton models cannot
explain the size of the excess. Some implications for flavor physics are briefly discussed
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