97 research outputs found
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Non-contact atomic-level interfacial force microscopy
The scanning force microscopies (notably the Atomic Force Microscope--AFM), because of their applicability to nearly all materials, are presently the most widely used of the scanning-probe techniques. However, the AFM uses a deflection sensor to measure sample/probe forces which suffers from an inherent mechanical instability that occurs when the rate of change of the force with respect to the interfacial separation becomes equal to the spring constant of the deflecting member. This instability dramatically limits the breadth of applicability of AFM-type techniques to materials problems. In the course of implementing a DOE sponsored basic research program in interfacial adhesion, a self-balancing force sensor concept has been developed and incorporated into an Interfacial Force Microscopy (IFM) system by Sandia scientists. This sensor eliminates the instability problem and greatly enhances the applicability of the scanning force-probe technique to a broader range of materials and materials parameters. The impact of this Sandia development was recognized in 1993 by a Department of Energy award for potential impact on DOE programs and by an R and D 100 award for one of the most important new products of 1994. However, in its present stage of development, the IFM is strictly a research-level tool and a CRADA was initiated in order to bring this sensor technology into wide-spread availability by making it accessible in the form of a commercial instrument. The present report described the goals, approach and results of this CRADA effort
Ac Stark Effects and Harmonic Generation in Periodic Potentials
The ac Stark effect can shift initially nonresonant minibands in
semiconductor superlattices into multiphoton resonances. This effect can result
in strongly enhanced generation of a particular desired harmonic of the driving
laser frequency, at isolated values of the amplitude.Comment: RevTeX, 10 pages (4 figures available on request), Preprint
UCSBTH-93-2
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Total Zinc Intake May Modify the Glucose-Raising Effect of a Zinc Transporter (SLC30A8) Variant
Objective: Many genetic variants have been associated with glucose homeostasis and type 2 diabetes in genome-wide association studies. Zinc is an essential micronutrient that is important for β-cell function and glucose homeostasis. We tested the hypothesis that zinc intake could influence the glucose-raising effect of specific variants. Research Design and Methods: We conducted a 14-cohort meta-analysis to assess the interaction of 20 genetic variants known to be related to glycemic traits and zinc metabolism with dietary zinc intake (food sources) and a 5-cohort meta-analysis to assess the interaction with total zinc intake (food sources and supplements) on fasting glucose levels among individuals of European ancestry without diabetes. Results: We observed a significant association of total zinc intake with lower fasting glucose levels (β-coefficient ± SE per 1 mg/day of zinc intake: −0.0012 ± 0.0003 mmol/L, summary P value = 0.0003), while the association of dietary zinc intake was not significant. We identified a nominally significant interaction between total zinc intake and the SLC30A8 rs11558471 variant on fasting glucose levels (β-coefficient ± SE per A allele for 1 mg/day of greater total zinc intake: −0.0017 ± 0.0006 mmol/L, summary interaction P value = 0.005); this result suggests a stronger inverse association between total zinc intake and fasting glucose in individuals carrying the glucose-raising A allele compared with individuals who do not carry it. None of the other interaction tests were statistically significant. Conclusions: Our results suggest that higher total zinc intake may attenuate the glucose-raising effect of the rs11558471 SLC30A8 (zinc transporter) variant. Our findings also support evidence for the association of higher total zinc intake with lower fasting glucose levels
Restriction of HIV-1 infection in sickle cell trait
Patients with sickle cell disease (SCD) have a lower risk for HIV-1 infection. We reported restriction of ex vivo HIV-1 infection in SCD peripheral blood mononuclear cells (PBMCs) that was due, in part, to the upregulation of antiviral, inflammatory, and hemolytic factors, including heme oxygenase-1 (HO-1). Here, we investigated whether individuals with sickle cell trait (SCT), who develop mild hemolysis, also restrict HIV-1 infection. Ex vivo infection of SCT PBMCs exhibited an approximately twofold reduction of HIV-1 replication and lower levels of HIV-1 reverse transcription products, 2-long terminal repeat circle, HIV-1 integration, and gag RNA expression. SCT PBMCs had higher HO-1 messenger RNA (mRNA) and protein levels and reduced ribonucleotide reductase 2 (RNR2) protein levels. HO-1 inhibition by tin porphyrin eliminated ex vivo HIV-1 restriction. Among Howard University clinic recruits, higher levels of HO-1 and RNR2 mRNA and lower HIV-1 env mRNA levels were found in SCT individuals living with HIV-1. To determine the population-level effect of SCT on HIV-1 prevalence, we assessed SCT among women living with HIV (WLH) in the WIHS (Women InteragencyHIV-1 Study). Among WIHS African-American participants, the prevalence of SCT was lower among women with HIV compared with uninfected women (8.7% vs 14.2%; odds ratio, 0.57; 95% confidence interval, 0.36-0.92; P = .020). WIHS WLH with SCT had higher levels of CD4+/CD8+ ratios over 20 years of follow-up (P = .003) than matched WLH without SCT. Together, our findings suggest that HIV-1 restriction factors, including HO-1 and RNR2, might restrict HIV-1 infection among individuals with SCT and limit the pathogenicity of HIV
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
All-sky search for long-duration gravitational wave transients with initial LIGO
We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society
On the progenitor of binary neutron star merger GW170817
On 2017 August 17 the merger of two compact objects with masses consistent with two neutron stars was discovered through gravitational-wave (GW170817), gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The optical source was associated with the early-type galaxy NGC 4993 at a distance of just ∼40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of ∼2 kpc away from the galaxy's center. We use this minimal set of facts and the mass posteriors of the two neutron stars to derive the first constraints on the progenitor of GW170817 at the time of the second supernova (SN). We generate simulated progenitor populations and follow the three-dimensional kinematic evolution from binary neutron star (BNS) birth to the merger time, accounting for pre-SN galactic motion, for considerably different input distributions of the progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not considerably tight, we find these constraints to be comparable to those for Galactic BNS progenitors. The derived constraints are very strongly influenced by the requirement of keeping the binary bound after the second SN and having the merger occur relatively close to the center of the galaxy. These constraints are insensitive to the galaxy's star formation history, provided the stellar populations are older than 1 Gyr
THE RATE OF BINARY BLACK HOLE MERGERS INFERRED FROM ADVANCED LIGO OBSERVATIONS SURROUNDING GW150914
A transient gravitational-wave signal, GW150914, was identi
fi
ed in the twin Advanced LIGO detectors on 2015
September 2015 at 09:50:45 UTC. To asse
ss the implications of this discovery,
the detectors remained in operation with
unchanged con
fi
gurations over a period of 39 days around the time of t
he signal. At the detection statistic threshold
corresponding to that observed for GW150914, our search of the 16 days of simultaneous two-detector observational
data is estimated to have a false-alarm rate
(
FAR
)
of
<
́
--
4.9 10 yr
61
, yielding a
p
-value for GW150914 of
<
́
-
210
7
. Parameter estimation follo
w-up on this trigger identi
fi
es its source as a binary black hole
(
BBH
)
merger
with component masses
(
)(
)
=
-
+
-
+
mm
M
,36,29
12
4
5
4
4
at redshift
=
-
+
z
0.09
0.04
0.03
(
median and 90% credible range
)
.
Here, we report on the constraints these observations place on the rate of BBH coalescences. Considering only
GW150914, assuming that all BBHs in the universe have the same masses and spins as this event, imposing a search
FAR threshold of 1 per 100 years, and assuming that the BBH merger rate is constant in the comoving frame, we infer a
90% credible range of merger rates between
–
--
2
53 Gpc yr
31
(
comoving frame
)
. Incorporating all search triggers that
pass a much lower threshold while accounting for the uncerta
inty in the astrophysical origin of each trigger, we estimate
a higher rate, ranging from
–
--
13 600 Gpc yr
31
depending on assumptions about the BBH mass distribution. All
together, our various rate estimat
es fall in the conservative range
–
--
2
600 Gpc yr
31
- …