9,402 research outputs found
The stochastic dynamics of nanoscale mechanical oscillators immersed in a viscous fluid
The stochastic response of nanoscale oscillators of arbitrary geometry
immersed in a viscous fluid is studied. Using the fluctuation-dissipation
theorem it is shown that deterministic calculations of the governing fluid and
solid equations can be used in a straightforward manner to directly calculate
the stochastic response that would be measured in experiment. We use this
approach to investigate the fluid coupled motion of single and multiple
cantilevers with experimentally motivated geometries.Comment: 5 pages, 5 figure
Fluctuation-dissipation ratios in the dynamics of self-assembly
We consider two seemingly very different self-assembly processes: formation
of viral capsids, and crystallization of sticky discs. At low temperatures,
assembly is ineffective, since there are many metastable disordered states,
which are a source of kinetic frustration. We use fluctuation-dissipation
ratios to extract information about the degree of this frustration. We show
that our analysis is a useful indicator of the long term fate of the system,
based on the early stages of assembly.Comment: 8 pages, 6 figure
Finite-temperature critical point of a glass transition
We generalize the simplest kinetically constrained model of a glass-forming
liquid by softening kinetic constraints, allowing them to be violated with a
small finite rate. We demonstrate that this model supports a first-order
dynamical (space-time) phase transition, similar to those observed with hard
constraints. In addition, we find that the first-order phase boundary in this
softened model ends in a finite-temperature dynamical critical point, which we
expect to be present in natural systems. We discuss links between this critical
point and quantum phase transitions, showing that dynamical phase transitions
in dimensions map to quantum transitions in the same dimension, and hence
to classical thermodynamic phase transitions in dimensions. We make these
links explicit through exact mappings between master operators, transfer
matrices, and Hamiltonians for quantum spin chains.Comment: 10 pages, 5 figure
First Results from a 1.3 cm EVLA Survey of Massive Protostellar Objects: G35.03+0.35
We have performed a 1.3 centimeter survey of 24 massive young stellar objects
(MYSOs) using the Expanded Very Large Array (EVLA). The sources in the sample
exhibit a broad range of massive star formation signposts including Infrared
Dark Clouds (IRDCs), UCHII regions, and extended 4.5 micron emission in the
form of Extended Green Objects (EGOs). In this work, we present results for
G35.03+0.35 which exhibits all of these phenomena. We simultaneously image the
1.3 cm ammonia (1,1) through (6,6) inversion lines, four methanol transitions,
two H recombination lines, plus continuum at 0.05 pc resolution. We find three
areas of thermal ammonia emission, two within the EGO (designated the NE and SW
cores) and one toward an adjacent IRDC. The NE core contains an UCHII region
(CM1) and a candidate HCHII region (CM2). A region of non-thermal, likely
masing ammonia (3,3) and (6,6) emission is coincident with an arc of 44 GHz
methanol masers. We also detect two new 25 GHz Class I methanol masers. A
complementary Submillimeter Array 1.3 mm continuum image shows that the
distribution of dust emission is similar to the lower-lying ammonia lines, all
peaking to the NW of CM2, indicating the likely presence of an additional MYSO
in this protocluster. By modeling the ammonia and 1.3 mm continuum data, we
obtain gas temperatures of 20-220 K and masses of 20-130 solar. The diversity
of continuum emission properties and gas temperatures suggest that objects in a
range of evolutionary states exist concurrently in this protocluster.Comment: To appear in Astrophysical Journal Letters Special Issue on the EVLA.
16 pages, 3 figures. Includes the complete version of Figure 3, which was
unable to fit into the journal article due to the number of panel
The Protocluster G18.67+0.03: A Test Case for Class I Methanol Masers as Evolutionary Indicators for Massive Star Formation
We present high angular resolution Submillimeter Array (SMA) and Karl G.
Jansky Very Large Array (VLA) observations of the massive protocluster
G18.67+0.03. Previously targeted in maser surveys of GLIMPSE Extended Green
Objects (EGOs), this cluster contains three Class I methanol maser sources,
providing a unique opportunity to test the proposed role of Class I masers as
evolutionary indicators for massive star formation. The millimeter observations
reveal bipolar molecular outflows, traced by 13CO(2-1) emission, associated
with all three Class I maser sources. Two of these sources (including the EGO)
are also associated with 6.7 GHz Class II methanol masers; the Class II masers
are coincident with millimeter continuum cores that exhibit hot core line
emission and drive active outflows, as indicated by the detection of SiO(5-4).
In these cases, the Class I masers are coincident with outflow lobes, and
appear as clear cases of excitation by active outflows. In contrast, the third
Class I source is associated with an ultracompact HII region, and not with
Class II masers. The lack of SiO emission suggests the 13CO outflow is a relic,
consistent with its longer dynamical timescale. Our data show that massive
young stellar objects associated only with Class I masers are not necessarily
young, and provide the first unambiguous evidence that Class I masers may be
excited by both young (hot core) and older (UC HII) MYSOs within the same
protocluster.Comment: Astrophysical Journal Letters, accepted. emulateapj, 7 pages
including 4 figures and 1 table. Figures compressed. v2: coauthor affiliation
updated, emulateapj versio
The application of the global isomorphism to the surface tension of the liquid-vapor interface of the Lennard-Jones fluids
In this communication we show that the surface tension of the real fluids of
the Lennard-Jones type can be obtained from the surface tension of the lattice
gas (Ising model) on the basis of the global isomorphism approach developed
earlier for the bulk properties.Comment: 8 pages, 6 figure
Origin of entropy convergence in hydrophobic hydration and protein folding
An information theory model is used to construct a molecular explanation why
hydrophobic solvation entropies measured in calorimetry of protein unfolding
converge at a common temperature. The entropy convergence follows from the weak
temperature dependence of occupancy fluctuations for molecular-scale volumes in
water. The macroscopic expression of the contrasting entropic behavior between
water and common organic solvents is the relative temperature insensitivity of
the water isothermal compressibility. The information theory model provides a
quantitative description of small molecule hydration and predicts a negative
entropy at convergence. Interpretations of entropic contributions to protein
folding should account for this result.Comment: Phys. Rev. Letts. (in press 1996), 3 pages, 3 figure
Gene Expression Signature in Adipose Tissue of Acromegaly Patients.
To study the effect of chronic excess growth hormone on adipose tissue, we performed RNA sequencing in adipose tissue biopsies from patients with acromegaly (n = 7) or non-functioning pituitary adenomas (n = 11). The patients underwent clinical and metabolic profiling including assessment of HOMA-IR. Explants of adipose tissue were assayed ex vivo for lipolysis and ceramide levels. Patients with acromegaly had higher glucose, higher insulin levels and higher HOMA-IR score. We observed several previously reported transcriptional changes (IGF1, IGFBP3, CISH, SOCS2) that are known to be induced by GH/IGF-1 in liver but are also induced in adipose tissue. We also identified several novel transcriptional changes, some of which may be important for GH/IGF responses (PTPN3 and PTPN4) and the effects of acromegaly on growth and proliferation. Several differentially expressed transcripts may be important in GH/IGF-1-induced metabolic changes. Specifically, induction of LPL, ABHD5, and NRIP1 can contribute to enhanced lipolysis and may explain the elevated adipose tissue lipolysis in acromegalic patients. Higher expression of TCF7L2 and the fatty acid desaturases FADS1, FADS2 and SCD could contribute to insulin resistance. Ceramides were not different between the two groups. In summary, we have identified the acromegaly gene expression signature in human adipose tissue. The significance of altered expression of specific transcripts will enhance our understanding of the metabolic and proliferative changes associated with acromegaly
The role of sonographic phenotyping in delivering an efficient non-invasive prenatal diagnosis (NIPD) service for FGFR3-related skeletal dysplasias
Objectives:
To evaluate the diagnostic yield of noninvasive prenatal diagnosis (NIPD) for FGFR3ârelated skeletal dysplasias and assess the accuracy of referrals based on sonographic findings to inform guidelines for referral.
Methods:
We retrospectively reviewed laboratory and referral records from 2012 to 2018 to ascertain all NIPD tests performed using our next generation sequencing panel to detect FGFR3 mutations. We calculated the diagnostic yield of the test overall and when subâdivided according to the phenotypic features identified on ultrasound before testing. Pregnancy outcomes were ascertained wherever possible from referring centers.
Results:
Of 335 tests, 261 were referred because of sonographic findings, of which 80 (31.3%) had a mutation. The diagnostic yield when short limbs were the only abnormal sonographic feature reported was 17.9% (30/168), increasing to 48.9% (23/47) in the presence of one, and 82.6% (19/23) in the presence of two or more characteristic features in addition to short limbs.
Conclusions:
Accurate sonographic phenotyping can maximise the diagnostic yield of NIPD in fetuses suspected to have FGFR3ârelated skeletal dysplasias. We suggest that clear guidelines for referral are necessary to increase benefits, decrease costs by preventing unnecessary NIPD, and potentially allow firstâline broader spectrum testing for fetuses where the aetiology may be more heterogeneous
Anisotropic spatially heterogeneous dynamics in a model glass-forming binary mixture
We calculated a four-point correlation function G_4(k,r;t) and the
corresponding structure factor S_4(k,q;t) for a model glass-forming binary
mixture. These functions measure the spatial correlations of the relaxation of
different particles. We found that these four-point functions are anisotropic
and depend on the angle between vectors k and r (or q). The anisotropy is the
strongest for times somewhat longer than the beta relaxation time but it is
quite pronounced even for times comparable to the alpha relaxation time,
tau_alpha. At the lowest temperatures S_4(k,q;tau_alpha) is strongly
anisotropic even for the smallest wavevector q accessible in our simulation
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