355 research outputs found
Coherent Diffractive Imaging Using Randomly Coded Masks
Coherent diffractive imaging (CDI) provides new opportunities for high
resolution X-ray imaging with simultaneous amplitude and phase contrast.
Extensions to CDI broaden the scope of the technique for use in a wide variety
of experimental geometries and physical systems. Here, we experimentally
demonstrate a new extension to CDI that encodes additional information through
the use of a series of randomly coded masks. The information gained from the
few additional diffraction measurements removes the need for typical
object-domain constraints; the algorithm uses prior information about the masks
instead. The experiment is performed using a laser diode at 532.2 nm, enabling
rapid prototyping for future X-ray synchrotron and even free electron laser
experiments. Diffraction patterns are collected with up to 15 different masks
placed between a CCD detector and a single sample. Phase retrieval is performed
using a convex relaxation routine known as "PhaseCut" followed by a variation
on Fienup's input-output algorithm. The reconstruction quality is judged via
calculation of phase retrieval transfer functions as well as by an object-space
comparison between reconstructions and a lens-based image of the sample. The
results of this analysis indicate that with enough masks (in this case 3 or 4)
the diffraction phases converge reliably, implying stability and uniqueness of
the retrieved solution
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Sex Hormone-Binding Globulin Levels Are Inversely Associated With Nonalcoholic Fatty Liver Disease in HIV-Infected and -Uninfected Men.
BackgroundNonalcoholic fatty liver disease (NAFLD) is a leading cause of liver disease worldwide. Elevated sex hormone-binding globulin (SHBG) levels have been observed in the setting of HIV and may protect against some metabolic disorders. We aimed to investigate whether higher SHBG levels may protect against NAFLD in men with/without HIV.MethodsNAFLD was assessed using noncontrast computed tomography in 530 men in the Multicenter AIDS Cohort Study (MACS) who drank <3 alcoholic drinks/d and were uninfected with chronic hepatitis C or B (340HIV+, 190HIV-). Morning serum samples were tested for SHBG, total testosterone (TT), and adiponectin. Multivariable logistic regression was used to assess associations between HIV, SHBG, TT, adiponectin, and NAFLD.ResultsMedian SHBG was highest among HIV+/NAFLD- men and lowest among HIV-/NAFLD+ men. Adjusted for demographics, HIV, visceral adiposity, HOMA-IR, TT, and PNPLA3 genotype, higher SHBG was associated with lower odds of NAFLD (odds ratio [OR], 0.52 per doubling; 95% confidence interval [CI], 0.34-0.80). In separate multivariable models without SHBG, HIV (OR, 0.46; 95% CI, 0.26-0.79) and higher adiponectin (OR, 0.66 per doubling; 95% CI, 0.49-0.89) were associated with lower NAFLD odds, whereas TT was not significantly associated (OR, 0.74 per doubling; 95% CI, 0.53-1.04). Adjusting for SHBG attenuated the associations of HIV (OR, 0.61; 95% CI, 0.34-1.08) and adiponectin (OR, 0.74; 95% CI, 0.54-1.02) with NAFLD.ConclusionsSHBG levels were higher among HIV+ men, were independently associated with lower NAFLD, and could partially explain the associations of HIV and higher adiponectin with lower NAFLD in our cohort. These findings suggest that SHBG may protect against NAFLD, supporting further prospective and mechanistic studies
Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa2Cu3O6.48
Resonant optical excitation of apical oxygen vibrational modes in the normal
state of underdoped YBa2Cu3O6+x induces a transient state with optical
properties similar to those of the equilibrium superconducting state. Amongst
these, a divergent imaginary conductivity and a plasma edge are transiently
observed in the photo-stimulated state. Femtosecond hard x-ray diffraction
experiments have been used in the past to identify the transient crystal
structure in this non-equilibrium state. Here, we start from these
crystallographic features and theoretically predict the corresponding
electronic rearrangements that accompany these structural deformations. Using
density functional theory, we predict enhanced hole-doping of the CuO2 planes.
The empty chain Cu dy2-z2 orbital is calculated to strongly reduce in energy,
which would increase c-axis transport and potentially enhance the interlayer
Josephson coupling as observed in the THz-frequency response. From these
calculations, we predict changes in the soft x-ray absorption spectra at the Cu
L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe
these changes in absorption at two photon energies along this spectrum, and
provide data consistent with these predictions.Comment: 20 pages with 6 figure
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
Factors Associated with Elevated ALT in an International HIV/HBV Co-Infected Cohort on Long-Term HAART
Previous studies have demonstrated that hepatitis B virus (HBV) infection increases the risk for ALT elevations in HIV-HBV co-infected patients during the first year of HAART; however, there is limited data on the prevalence of ALT elevations with prolonged HAART in this patient group.To identify factors associated with ALT elevations in an HIV-HBV co-infected cohort receiving prolonged HAART, data from 143 co-infected patients on HAART enrolled in an international HIV-HBV co-infected cohort where ALT measurements were obtained every 6 months was analysed. A person-visit analysis was used to determine frequency of ALT elevation (≥ 2.5×ULN) at each visit. Factors associated with ALT elevation were determined using multivariate logistic regression with generalized estimating equations to account for correlated data. The median time on HAART at the end of follow-up was 5.6 years (range 0.4-13.3) years. During follow-up, median ALT was 36 U/L with 10.6% of person-visits classified as having ALT elevation. Most ALT elevations were grade 2 (86.5%), with only 13.5% of all ALT elevations grade 3 or higher. Univariate associations with ALT elevation (p<0.05) included history of AIDS, HBV DNA ≥ 2,000 IU/ml, HBeAg positive, study visit CD4 <200 cells/ml and nadir CD4 <200 cells/ml. In the multivariate analysis, only study visit CD4 <200 cells/ml (OR 2.07, 95%CI 1.04-4.11, p = 0.04) and HBeAg positive status (OR 2.22, 95%CI 1.03-4.79, p = 0.04) were independently associated with ALT elevation.In this HIV-HBV co-infected cohort, elevated ALT after >1 year of HAART was uncommon, and severe ALT elevations were rare. HIV-HBV co-infected patients on long-term HAART who are either HBeAg positive or have a CD4 count of <200 cells/ml are at increased risk for ALT elevations
Improvement of Neuromuscular Synaptic Phenotypes without Enhanced Survival and Motor Function in Severe Spinal Muscular Atrophy Mice Selectively Rescued in Motor Neurons
In the inherited childhood neuromuscular disease spinal muscular atrophy (SMA), lower motor neuron death and severe muscle weakness result from the reduction of the ubiquitously expressed protein survival of motor neuron (SMN). Although SMA mice recapitulate many features of the human disease, it has remained unclear if their short lifespan and motor weakness are primarily due to cell-autonomous defects in motor neurons. Using Hb9(Cre) as a driver, we selectively raised SMN expression in motor neurons in conditional SMAΔ7 mice. Unlike a previous study that used choline acetyltransferase (ChAT(Cre+) ) as a driver on the same mice, and another report that used Hb9(Cre) as a driver on a different line of conditional SMA mice, we found no improvement in survival, weight, motor behavior and presynaptic neurofilament accumulation. However, like in ChAT(Cre+) mice, we detected rescue of endplate size and mitigation of neuromuscular junction (NMJ) denervation status. The rescue of endplate size occurred in the absence of an increase in myofiber size, suggesting endplate size is determined by the motor neuron in these animals. Real time-PCR showed that the expression of spinal cord SMN transcript was sharply reduced in Hb9(Cre+) SMA mice relative to ChAT(Cre+) SMA mice. This suggests that our lack of overall phenotypic improvement is most likely due to an unexpectedly poor recombination efficiency driven by Hb9(Cre) . Nonetheless, the low levels of SMN were sufficient to rescue two NMJ structural parameters indicating that these motor neuron cell autonomous phenotypes are very sensitive to changes in motoneuronal SMN levels. Our results directly suggest that even those therapeutic interventions with very modest effects in raising SMN in motor neurons may provide mitigation of neuromuscular phenotypes in SMA patients
Comparative Analysis of the Frequency and Distribution of Stem and Progenitor Cells in the Adult Mouse Brain
cells (NSCs) and progenitor cells, but it cannot discriminate
between these two populations. Given two assays
have purported to overcome this shortfall, we performed
a comparative analysis of the distribution and frequency
of NSCs and progenitor cells detected in 400 m coronal
segments along the ventricular neuraxis of the adult
mouse brain using the neurosphere assay, the neural
colony forming cell assay (N-CFCA), and label-retaining
cell (LRC) approach. We observed a large variation in the
number of progenitor/stem cells detected in serial sections
along the neuraxis, with the number of neurosphereforming
cells detected in individual 400 m sections varying
from a minimum of eight to a maximum of 891
depending upon the rostral-caudal coordinate assayed.
Moreover, the greatest variability occurred in the rostral
portion of the lateral ventricles, thereby explaining the
large variation in neurosphere frequency previously reported.
Whereas the overall number of neurospheres
(3730 276) or colonies (4275 124) we detected along
the neuraxis did not differ significantly, LRC numbers
were significantly reduced (1186 188, 7 month chase) in
comparison to both total colonies and neurospheres.
Moreover, approximately two orders of magnitude fewer
NSC-derived colonies (50 10) were detected using the
N-CFCA as compared to LRCs. Given only 5% of the
LRCs are cycling (BrdU/Ki-67) or competent to divide
(BrdU/Mcm-2), and proliferate upon transfer to culture,
it is unclear whether this technique selectively detects
endogenous NSCs. Overall, caution should be taken
with the interpretation and employment of all these techniques
Spontaneous fluctuations in a magnetic Fe/Gd skyrmion lattice
Magnetic skyrmions are topological spin textures that exhibit classical or quantum quasiparticle behavior. A substantial amount of research has occurred in this field, both because of their unique electromagnetic properties and potential application for future nonvolatile memory storage applications, as well as fundamental questions on their topology and unique magnetic phases. Here, we investigate the fluctuation properties of a magnetic Fe/Gd skyrmion lattice, using short-pulsed x rays. We first measure spontaneous fluctuations of the skyrmion lattice phase and find an inherent, collective mode showing an underdamped oscillation with a relaxation of a couple of nanoseconds. Further observations track the response towards the continuous phase transition and a critical-like slowing down of fluctuations is observed well before the critical point. These results suggest that the skyrmion lattice phase never fully freezes into a static crystal. This constant state of fluctuation indicates that the physics of topological magnetic phases may have more in common with high-temperature superconductors with disorder
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