440 research outputs found
Direct observation of molecular cooperativity near the glass transition
We describe direct observations of molecular cooperativity near the glass
transition in poly-vinyl-acetate (PVAc), through nanometer-scale probing of
dielectric fluctuations. Molecular clusters switched spontaneously between two
to four distinct configurations, producing complex random-telegraph-signals
(RTS). Analysis of the RTS and their power spectra shows that individual
clusters exhibit both transient dynamical heterogeneity and non-exponential
kinetics.Comment: 14 pages pdf, need Acrobat Reade
Temperature- and thickness-dependent elastic moduli of polymer thin films
The mechanical properties of polymer ultrathin films are usually different from those of their counterparts in bulk. Understanding the effect of thickness on the mechanical properties of these films is crucial for their applications. However, it is a great challenge to measure their elastic modulus experimentally with in situ heating. In this study, a thermodynamic model for temperature- (T) and thickness (h)-dependent elastic moduli of polymer thin films Ef(T,h) is developed with verification by the reported experimental data on polystyrene (PS) thin films. For the PS thin films on a passivated substrate, Ef(T,h) decreases with the decreasing film thickness, when h is less than 60 nm at ambient temperature. However, the onset thickness (h*), at which thickness Ef(T,h) deviates from the bulk value, can be modulated by T. h* becomes larger at higher T because of the depression of the quenching depth, which determines the thickness of the surface layer δ
Fast core rotation in red-giant stars revealed by gravity-dominated mixed modes
When the core hydrogen is exhausted during stellar evolution, the central
region of a star contracts and the outer envelope expands and cools, giving
rise to a red giant, in which convection occupies a large fraction of the star.
Conservation of angular momentum requires that the cores of these stars rotate
faster than their envelopes, and indirect evidence supports this. Information
about the angular momentum distribution is inaccessible to direct observations,
but it can be extracted from the effect of rotation on oscillation modes that
probe the stellar interior. Here, we report the detection of non-rigid rotation
in the interiors of red-giant stars by exploiting the rotational frequency
splitting of recently detected mixed modes. We demonstrate an increasing
rotation rate from the surface of the star to the stellar core. Comparing with
theoretical stellar models, we conclude that the core must rotate at least ten
times faster than the surface. This observational result confirms the
theoretical prediction of a steep gradient in the rotation profile towards the
deep stellar interior.Comment: to appear as a Letter to Natur
The Initial Mass Function in the Galactic Center
The Galactic Center contains the most massive young clusters in the Galaxy
and serves as the closest example of a massive starburst region. Our recent
results suggest that the Galactic Center environment produces massive clusters
with relatively flat initial mass functions, as might be expected on
theoretical grounds. I will discuss these recent results, along with evidence
for star formation in the immediate vicinity of the super massive black hole at
the Galactic Center. The results of this work might be useful in extrapolating
to other galactic centers with similar conditions, as well as other starburst
regions
The development of a protoplanetary disk from its natal envelope
Class 0 protostars, the youngest type of young stellar objects, show many signs of rapid development from their initial, spheroidal configurations, and therefore are studied intensively for details of the formation of protoplanetary disks within protostellar envelopes. At millimetre wavelengths, kinematic signatures of collapse have been observed in several such protostars, through observations of molecular lines that probe their outer envelopes. It has been suggested that one or more components of the proto-multiple system NGC 1333-IRAS 4 (refs 1, 2) may display signs of an embedded region that is warmer and denser than the bulk of the envelope(3,4). Here we report observations that reveal details of the core on Solar System dimensions. We detect in NGC 1333-IRAS 4B a rich emission spectrum of H2O, at wavelengths 20-37 mu m, which indicates an origin in extremely dense, warm gas. We can model the emission as infall from a protostellar envelope onto the surface of a deeply embedded, dense disk, and therefore see the development of a protoplanetary disk. This is the only example of mid-infrared water emission from a sample of 30 class 0 objects, perhaps arising from a favourable orientation; alternatively, this may be an early and short-lived stage in the evolution of a protoplanetary disk.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62894/1/nature06087.pd
Studying the Underlying Event in Drell-Yan and High Transverse Momentum Jet Production at the Tevatron
We study the underlying event in proton-antiproton collisions by examining
the behavior of charged particles (transverse momentum pT > 0.5 GeV/c,
pseudorapidity |\eta| < 1) produced in association with large transverse
momentum jets (~2.2 fb-1) or with Drell-Yan lepton-pairs (~2.7 fb-1) in the
Z-boson mass region (70 < M(pair) < 110 GeV/c2) as measured by CDF at 1.96 TeV
center-of-mass energy. We use the direction of the lepton-pair (in Drell-Yan
production) or the leading jet (in high-pT jet production) in each event to
define three regions of \eta-\phi space; toward, away, and transverse, where
\phi is the azimuthal scattering angle. For Drell-Yan production (excluding the
leptons) both the toward and transverse regions are very sensitive to the
underlying event. In high-pT jet production the transverse region is very
sensitive to the underlying event and is separated into a MAX and MIN
transverse region, which helps separate the hard component (initial and
final-state radiation) from the beam-beam remnant and multiple parton
interaction components of the scattering. The data are corrected to the
particle level to remove detector effects and are then compared with several
QCD Monte-Carlo models. The goal of this analysis is to provide data that can
be used to test and improve the QCD Monte-Carlo models of the underlying event
that are used to simulate hadron-hadron collisions.Comment: Submitted to Phys.Rev.
The hypoxic cancer secretome induces pre-metastatic bone lesions through lysyl oxidase
Tumour metastasis is a complex process involving reciprocal interplay
between cancer cells and host stroma at both primary and secondary
sites, and is strongly influenced by microenvironmental
factors such as hypoxia. Tumour-secreted proteins play a crucial role
in these interactions and present strategic therapeutic potential.
Metastasis of breast cancer to the bone affects approximately 85%
of patients with advanced disease and renders them largely untreatable. Specifically, osteolytic bone lesions, where bone is destroyed,
lead to debilitating skeletal complications and increased patient morbidity
and mortality. The molecular interactions governing the
early events of osteolytic lesion formation are currently unclear.
Here we show hypoxia to be specifically associated with bone relapse
in patients with oestrogen-receptor negative breast cancer. Global
quantitative analysis of the hypoxic secretome identified lysyl oxidase
(LOX) as significantly associated with bone-tropism and relapse.
High expression of LOX in primary breast tumours or systemic delivery
of LOX leads to osteolytic lesion formation whereas silencing or
inhibition of LOX activity abrogates tumour-driven osteolytic lesion
formation. We identify LOX as a novel regulator of NFATc1-driven
osteoclastogenesis,independent of RANK ligand, which disrupts normal
bone homeostasisleading to the formation of focal pre-metastatic
lesions. We show that these lesions subsequently provide a platform
for circulating tumour cells to colonize and form bone metastases.
Our study identifies a novel mechanism of regulation of bone homeostasis
and metastasis, opening up opportunities for novel therapeutic
intervention with important clinical implications
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
Background
A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.
Methods
Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendall’s tau for dichotomous variables, or Jonckheere–Terpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.
Results
A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both p < 0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROC = 0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all p < 0.001).
Conclusion
We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty
Measurement of Lifetime and Decay-Width Difference in B0s -> J/psi phi Decays
We measure the mean lifetime, tau=2/(Gamma_L+Gamma_H), and the width
difference, DeltaGamma=Gamma_L-Gamma_H, of the light and heavy mass eigenstates
of the B0s meson, B0sL and B0sH, in B0s -> J/psi phi decays using 1.7 fb^-1 of
data collected with the CDF II detector at the Fermilab Tevatron ppbar
collider. Assuming CP conservation, a good approximation for the B0s system in
the Standard Model, we obtain DeltaGamma = 0.076^+0.059_-0.063 (stat.) +- 0.006
(syst.) ps^-1 and tau = 1.52 +- 0.04 (stat.) +- 0.02 (syst.) ps, the most
precise measurements to date. Our constraints on the weak phase and DeltaGamma
are consistent with CP conservation.
Dedicated to the memory of our dear friend and colleague, Michael P. Schmid
Limits on Anomalous Triple Gauge Couplings in ppbar Collisions at sqrt{s}=1.96 TeV
We present a search for anomalous triple gauge couplings (ATGC) in WW and WZ
boson production. The boson pairs are produced in ppbar collisions at
sqrt{s}=1.96 TeV, and the data sample corresponds to 350 pb-1 of integrated
luminosity collected with the CDF II detector at the Fermilab Tevatron. In this
search one W decays to leptons, and the other boson (W or Z) decays
hadronically. Combining with a previously published CDF measurement of Wgamma
boson production yields ATGC limits of -0.18 < lambda < 0.17 and -0.46 < Delta
kappa < 0.39 at the 95% confidence level, using a cut-off scale Lambda=1.5 TeV.Comment: 7 pages, 3 figures. Submitted to Phys. Rev.
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