1,803 research outputs found
The bend stiffness of S-DNA
We formulate and solve a two-state model for the elasticity of nicked,
double-stranded DNA that borrows features from both the Worm Like Chain and the
Bragg--Zimm model. Our model is computationally simple, and gives an excellent
fit to recent experimental data through the entire overstretching transition.
The fit gives the first value for the bending stiffness of the overstretched
state as about 10 nm*kbt, a value quite different from either B-form or
single-stranded DNA.Comment: 7 pages, 1 figur
Critical behaviour in the nonlinear elastic response of hydrogels
In this paper we study the elastic response of synthetic hydrogels to an
applied shear stress. The hydrogels studied here have previously been shown to
mimic the behaviour of biopolymer networks when they are sufficiently far above
the gel point. We show that near the gel point they exhibit an elastic response
that is consistent with the predicted critical behaviour of networks near or
below the isostatic point of marginal stability. This point separates rigid and
floppy states, distinguished by the presence or absence of finite linear
elastic moduli. Recent theoretical work has also focused on the response of
such networks to finite or large deformations, both near and below the
isostatic point. Despite this interest, experimental evidence for the existence
of criticality in such networks has been lacking. Using computer simulations,
we identify critical signatures in the mechanical response of sub-isostatic
networks as a function of applied shear stress. We also present experimental
evidence consistent with these predictions. Furthermore, our results show the
existence of two distinct critical regimes, one of which arises from the
nonlinear stretch response of semi-flexible polymers.
Combined esophageal intraluminal impedance, pH and skin conductance monitoring to detect discomfort in GERD infants
BACKGROUND: The clinical significance of weakly acidic reflux in infants is unclear. Skin conductance is a novel not-invasive method to evaluate discomfort. The aim of our study was to evaluate reflux-induced discomfort in infants with gastroesophageal reflux disease using simultaneously combined skin conductance and esophageal multichannel intraluminal impedance and pH monitoring. METHODOLOGY/PRINCIPAL FINDINGS: Infants with gastroesophageal reflux symptoms were investigated for almost 20 hours divided into 120-second intervals. Temporal relationships between refluxes and discomfort were evaluated calculating the symptom association probability. Twelve infants aged 17-45 days were studied. Out of 194.38 hours of adequate artifact-free MII/pH and skin conductance monitoring, 584 reflux events were observed; 35.78% were positive for stress, of which 16.27% were acid and 83.73% weakly acidic. A significant association between refluxes and discomfort (p<0.05) was present in all infants. The intervals with reflux events showed increased skin conductance values compared to reflux-free intervals (p<0.001); SC values were similar for acid and weakly acidic reflux events. CONCLUSION/SIGNFICANCE: Discomfort was significantly associated with reflux events and did not differ between weakly acidic and acid refluxes. Our results may raise concerns about the over-prescription use of antacid drugs in the management of gastroesophageal reflux symptoms in infancy
Assessing direct contributions of morphological awareness and prosodic sensitivity to children’s word reading and reading comprehension
We examined the independent contributions of prosodic sensitivity and morphological awareness to word reading, text reading accuracy, and reading comprehension. We did so in a longitudinal study of English-speaking children (N = 70). At 5 to 7 years of age, children completed the metalinguistic measures along with control measures of phonological awareness and vocabulary. Children completed the reading measures two years later. Morphological awareness, but not prosodic sensitivity made a significant independent contribution to word reading, text reading accuracy and reading comprehension. The effects of morphological awareness on reading comprehension remained after controls for word reading. These results suggest that morphological awareness needs to be considered seriously in models of reading development and that prosodic sensitivity might have primarily indirect relations to reading outcomes.
Keywords: Morphological Awareness; Prosody; Word Reading; Reading Comprehension
Measurement of neutron capture on Ca at thermal and thermonuclear energies
At the Karlsruhe pulsed 3.75\,MV Van de Graaff accelerator the thermonuclear
Ca(n,)Ca(8.72\,min) cross section was measured by the
fast cyclic activation technique via the 3084.5\,keV -ray line of the
Ca-decay. Samples of CaCO enriched in Ca by 77.87\,\% were
irradiated between two gold foils which served as capture standards. The
capture cross-section was measured at the neutron energies 25, 151, 176, and
218\,keV, respectively. Additionally, the thermal capture cross-section was
measured at the reactor BR1 in Mol, Belgium, via the prompt and decay
-ray lines using the same target material. The
Ca(n,)Ca cross-section in the thermonuclear and thermal
energy range has been calculated using the direct-capture model combined with
folding potentials. The potential strengths are adjusted to the scattering
length and the binding energies of the final states in Ca. The small
coherent elastic cross section of Ca+n is explained through the nuclear
Ramsauer effect. Spectroscopic factors of Ca have been extracted from
the thermal capture cross-section with better accuracy than from a recent (d,p)
experiment. Within the uncertainties both results are in agreement. The
non-resonant thermal and thermonuclear experimental data for this reaction can
be reproduced using the direct-capture model. A possible interference with a
resonant contribution is discussed. The neutron spectroscopic factors of
Ca determined from shell-model calculations are compared with the values
extracted from the experimental cross sections for Ca(d,p)Ca and
Ca(n,)Ca.Comment: 15 pages (uses Revtex), 7 postscript figures (uses psfig), accepted
for publication in PRC, uuencoded tex-files and postscript-files also
available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Ca.u
Quantum transport through a DNA wire in a dissipative environment
Electronic transport through DNA wires in the presence of a strong
dissipative environment is investigated. We show that new bath-induced
electronic states are formed within the bandgap. These states show up in the
linear conductance spectrum as a temperature dependent background and lead to a
crossover from tunneling to thermal activated behavior with increasing
temperature. Depending on the strength of the electron-bath coupling, the
conductance at the Fermi level can show a weak exponential or even an algebraic
length dependence. Our results suggest a new environmental-induced transport
mechanism. This might be relevant for the understanding of molecular conduction
experiments in liquid solution, like those recently performed on poly(GC)
oligomers in a water buffer (B. Xu et al., Nano Lett 4, 1105 (2004)).Comment: 5 pages, 3 figure
Weak Interaction Studies with 6He
The 6He nucleus is an ideal candidate to study the weak interaction. To this
end we have built a high-intensity source of 6He delivering ~10^10 atoms/s to
experiments. Taking full advantage of that available intensity we have
performed a high-precision measurement of the 6He half-life that directly
probes the axial part of the nuclear Hamiltonian. Currently, we are preparing a
measurement of the beta-neutrino angular correlation in 6He beta decay that
will allow to search for new physics beyond the Standard Model in the form of
tensor currents.Comment: 5 pages, 4 figures, proceedings for the Eleventh Conference on the
Intersections of Particle and Nuclear Physics (CIPANP 2012
Mesoscopic models for DNA stretching under force: new results and comparison to experiments
Single molecule experiments on B-DNA stretching have revealed one or two
structural transitions, when increasing the external force. They are
characterized by a sudden increase of DNA contour length and a decrease of the
bending rigidity. It has been proposed that the first transition, at forces of
60--80 pN, is a transition from B to S-DNA, viewed as a stretched duplex DNA,
while the second one, at stronger forces, is a strand peeling resulting in
single stranded DNAs (ssDNA), similar to thermal denaturation. But due to
experimental conditions these two transitions can overlap, for instance for
poly(dA-dT). We derive analytical formula using a coupled discrete worm like
chain-Ising model. Our model takes into account bending rigidity, discreteness
of the chain, linear and non-linear (for ssDNA) bond stretching. In the limit
of zero force, this model simplifies into a coupled model already developed by
us for studying thermal DNA melting, establishing a connexion with previous
fitting parameter values for denaturation profiles. We find that: (i) ssDNA is
fitted, using an analytical formula, over a nanoNewton range with only three
free parameters, the contour length, the bending modulus and the monomer size;
(ii) a surprisingly good fit on this force range is possible only by choosing a
monomer size of 0.2 nm, almost 4 times smaller than the ssDNA nucleobase
length; (iii) mesoscopic models are not able to fit B to ssDNA (or S to ss)
transitions; (iv) an analytical formula for fitting B to S transitions is
derived in the strong force approximation and for long DNAs, which is in
excellent agreement with exact transfer matrix calculations; (v) this formula
fits perfectly well poly(dG-dC) and -DNA force-extension curves with
consistent parameter values; (vi) a coherent picture, where S to ssDNA
transitions are much more sensitive to base-pair sequence than the B to S one,
emerges.Comment: 14 pages, 9 figure
Suicides among Danish cancer patients 1971–1999
Compared to the general population, the suicide risk among Danish cancer patients diagnosed in 1971–1986 was increased by 50% for men and 30% for women. We updated the earlier study to evaluate both long-term and recent trends in the suicide risk. Cancer patients with a first cancer diagnosed between 1971 and 1999 in Denmark were followed-up for completed suicide through 1999. Excluding nonmelanoma skin cancer, 564 508 cancer patients were included and 1241 suicides observed. Both the standardised mortality ratio (SMR) of suicide relative to the general population and the suicide rates were analysed with Poisson regression methods. The overall SMR was increased to 1.7 (95% CI. 1.6–1.9) for men and 1.4 (95% CI: 1.3–1.5) for women. Following the cancer diagnosis, the suicide risk was highest in the first 3 months for men and between months 3 and 12 for women. The risk was higher for nonlocalised cancer and for cancers with perceived poor prognosis. Breast cancer patients had a higher risk than other cancer patients with similar good prognosis. The suicide rates among cancer patients decreased with calendar time, but less so than the rates in the general population. The suicide risk among cancer patients has not decreased as much as in the Danish population and reasons for this should be explored. Breast cancer might be believed by patients to be more life threatening than it is. Assessment and treatment of depression could improve the quality of life for cancer patients who suffer from unrecognised depressions and in turn reduce the risk of suicide in cancer patients
CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1
We present details of the CARMA Large Area Star Formation Survey (CLASSy),
while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that
spectrally imaged N2H+, HCO+, and HCN (J=1-0 transitions) across over 800
square arcminutes of the Perseus and Serpens Molecular Clouds. The observations
have angular resolution near 7" and spectral resolution near 0.16 km/s. We
imaged ~150 square arcminutes of Barnard 1, focusing on the main core, and the
B1 Ridge and clumps to its southwest. N2H+ shows the strongest emission, with
morphology similar to cool dust in the region, while HCO+ and HCN trace several
molecular outflows from a collection of protostars in the main core. We
identify a range of kinematic complexity, with N2H+ velocity dispersions
ranging from ~0.05-0.50 km/s across the field. Simultaneous continuum mapping
at 3 mm reveals six compact object detections, three of which are new
detections. A new non-binary dendrogram algorithm is used to analyze dense gas
structures in the N2H+ position-position-velocity (PPV) cube. The projected
sizes of dendrogram-identified structures range from about 0.01-0.34 pc.
Size-linewidth relations using those structures show that non-thermal
line-of-sight velocity dispersion varies weakly with projected size, while rms
variation in the centroid velocity rises steeply with projected size. Comparing
these relations, we propose that all dense gas structures in Barnard 1 have
comparable depths into the sky, around 0.1-0.2 pc; this suggests that
over-dense, parsec-scale regions within molecular clouds are better described
as flattened structures rather than spherical collections of gas. Science-ready
PPV cubes for Barnard 1 molecular emission are available for download.Comment: Accepted to The Astrophysical Journal (ApJ), 51 pages, 27 figures
(some with reduced resolution in this preprint); Project website is at
http://carma.astro.umd.edu/class
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