4,276 research outputs found
Recommended from our members
Backbone-free duplex-stacked monomer nucleic acids exhibiting Watson-Crick selectivity.
We demonstrate that nucleic acid (NA) mononucleotide triphosphates (dNTPs and rNTPs), at sufficiently high concentration and low temperature in aqueous solution, can exhibit a phase transition in which chromonic columnar liquid crystal ordering spontaneously appears. Remarkably, this polymer-free state exhibits, in a self-assembly of NA monomers, the key structural elements of biological nucleic acids, including: long-ranged duplex stacking of base pairs, complementarity-dependent partitioning of molecules, and Watson-Crick selectivity, such that, among all solutions of adenosine, cytosine, guanine, and thymine NTPs and their binary mixtures, duplex columnar ordering is most stable in the A-T and C-G combinations
Jail Visitation: An Assessment of Organizational Policy and Information Availability
Jail inmates face substantial emotional, economic, legal, and other challenges when they are incarcerated. The extent to which they are able to maintain contacts with individuals on the outside can substantially determine how well they cope with these concerns, and visitation is the primary way that such links may be maintained. To date, no systematic assessment of jail visitation policies has been conducted. The current study examined the availability of visitation policy information and the content of policies for national samples of large and small jails. The results suggest that large jails provide more opportunities for visitation and that they provide more information than small jails. Overall, there exists an opportunity for jails to substantially increase the availability of crucial visitation information. Policy implications are discussed
Superconductivity induced by spark erosion in ZrZn2
We show that the superconductivity observed recently in the weak itinerant
ferromagnet ZrZn2 [C. Pfleiderer et al., Nature (London) 412, 58 (2001)] is due
to remnants of a superconducting layer induced by spark erosion. Results of
resistivity, susceptibility, specific heat and surface analysis measurements on
high-quality ZrZn2 crystals show that cutting by spark erosion leaves a
superconducting surface layer. The resistive superconducting transition is
destroyed by chemically etching a layer of 5 microns from the sample. No
signature of superconductivity is observed in rho(T) of etched samples at the
lowest current density measured, J=675 Am-2, and at T < 45 mK. EDX analysis
shows that spark-eroded surfaces are strongly Zn depleted. The simplest
explanation of our results is that the superconductivity results from an alloy
with higher Zr content than ZrZn2.Comment: Final published versio
Ruptured heterotopic pregnancy presenting as hemorrhagic shock
Background: Heterotopic pregnancy is a rare event consisting of simultaneous intrauterine and extrauterine pregnancies. If undiagnosed, it is probable the patient will present to an Emergency Department and require emergent care.
Case Report: A 25 year-old woman arrived at the Emergency Department at 14 weeks gestation reporting sharp abdominal cramping and pelvic pain with a history of current tobacco use. Trans-abdominal ultrasound revealed a viable intrauterine pregnancy consistent with 14 weeks, closed cervix with free fluid noted in pelvis, and no evidence of ovarian torsion. Over the next three hours, the patient’s condition deteriorated and hemoglobin levels dropped. The surgeon on call was consulted and suspected ruptured hepatic adenoma versus hepatic hemangioma versus visceral aneurysm. A laparotomy was emergently performed with supraceliac control of aorta to permit resuscitation, and the right and left upper quadrants of the abdominal cavity were investigated without discovery of bleeding source. Further investigation revealed ruptured left tubal ectopic pregnancy and a partial salpingectomy was performed.
Conclusions: This case serves as a clinical reminder that while heterotopic pregnancy is thought to be rare, when a patient presents with known intrauterine pregnancy and abdominal pain, heterotopic pregnancy should be included in the differential diagnosis. More common use of assisted reproductive technology may increase the incidence of heterotopic pregnancies, making familiarity with the signs, symptoms, and risk factors for this condition important
Size-selective predation by three estuarine zooplanktivorous fish species
Zooplanktivorous fish are a key link between abundant zooplankton and higher
trophic levels but the foraging behaviour of zooplanktivorous fish is not fully understood.
Selective feeding behaviours have been observed, with many species of planktivorous fish
targeting certain species and sizes of zooplankton for prey. However, why certain size classes
of zooplankton are preferred remains unclear. Aim. This study investigated prey selection by
three zooplanktivorous fish species through the lens of optimal foraging theory. Methods. We
assessed the size structure of zooplankton in the environment and compared this with the size
distribution of zooplankton in gut contents from three zooplanktivorous fish. Key results. The
targeted prey size of Atypichthys strigatus and Scorpis lineolata aligns with the prey size classes in the
environment that contain the highest overall biomass. Trachurus novaezelandiae showed little
evidence of targeting these size classes. Conclusions. These prey sizes therefore represent the
most efficient prey to target because the return on foraging effort is greatest. By contrast,
T. novaezelandiae showed only an underselection of large and small prey. Implications. By
incorporating this information on this key trophic link between zooplankton and fish, ecosystem
models could better resolve the size dependant predation, particularly in size-based models
Electron and ion stagnation at the collision front between two laser produced plasmas
We report results from a combined optical interferometric and spectrally resolved imaging study on colliding laser produced aluminium plasmas. A Nomarski interferometer was used to probe the spatio-temporal distribution of electron densities at the collision front. Analysis of the resulting interferograms reveals the formation and evolution of a localized electron density feature with a well-defined profile reminiscent of a stagnation layer. Electron stagnation begins at a time delay of 10 ns after the peak of the plasma generating laser pulse. The peak electron density was found to exceed 10^19 cm^−3 and the layer remained well defined up to a time delay of ca 100 ns. Temporally and spectrally resolved optical imaging was also undertaken, to compare the Al^+ ion distribution with that of the 2D electron density profile. This revealed nascent stagnation of singly charged ions at a delay time of 20 ns. We attribute these results to the effects of space charge separation in the seed plasma plumes
Some Directions beyond Traditional Quantum Secret Sharing
We investigate two directions beyond the traditional quantum secret sharing
(QSS). First, a restriction on QSS that comes from the no-cloning theorem is
that any pair of authorized sets in an access structure should overlap. From
the viewpoint of application, this places an unnatural constraint on secret
sharing. We present a generalization, called assisted QSS (AQSS), where access
structures without pairwise overlap of authorized sets is permissible, provided
some shares are withheld by the share dealer. We show that no more than
withheld shares are required, where is the minimum number
of {\em partially linked classes} among the authorized sets for the QSS. Our
result means that such applications of QSS need not be thwarted by the
no-cloning theorem. Secondly, we point out a way of combining the features of
QSS and quantum key distribution (QKD) for applications where a classical
information is shared by quantum means. We observe that in such case, it is
often possible to reduce the security proof of QSS to that of QKD.Comment: To appear in Physica Scripta, 7 pages, 1 figure, subsumes
arXiv:quant-ph/040720
Single or Double Degenerate Progenitors? Searching for Shock Emission in the SDSS-II Type Ia Supernovae
From the set of nearly 500 spectroscopically confirmed type~Ia supernovae and
around 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108
confirmed SNe Ia with well-observed early-time light curves to search for
signatures from shock interaction of the supernova with a companion star. No
evidence for shock emission is seen; however, the cadence and photometric noise
could hide a weak shock signal. We simulate shocked light curves using SN Ia
templates and a simple, Gaussian shock model to emulate the noise properties of
the SDSS-II sample and estimate the detectability of the shock interaction
signal as a function of shock amplitude, shock width, and shock fraction. We
find no direct evidence for shock interaction in the rest-frame -band, but
place an upper limit on the shock amplitude at 9% of supernova peak flux ( mag). If the single degenerate channel dominates type~Ia progenitors,
this result constrains the companion stars to be less than about 6
on the main sequence, and strongly disfavors red giant companions.Comment: 28 pages, 3 figure
Age and growth of Pomatomus saltatrix in the south-western Pacific Ocean (eastern Australia), with a global comparison
Context: Pomatomus saltatrix is one of few globally distributed pelagic mesopredators that is exploited heavily throughout its range. Despite the implementation of management strategies, the south-western Pacific Ocean (eastern Australian) population has few published estimates of the key life-history parameters including growth.
Aims: To estimate the age and growth of P. saltatrix in the south-western Pacific and compare these with the age and growth in other populations.
Methods: Age estimates were made using whole otolith readings and an age–length key was used with a length frequency distribution to estimate the age structure of the population. Eight different growth models were compared within a Bayesian framework for both juvenile and overall growth.
Key results: The Schnute growth equation provided the best fit for overall growth and yielded parameter values of a = −0.15, b = 2.56, Size-at-age 1 = 24.38-cm fork length (FL) and Size-at-age 4 = 47.36 cm FL.
Conclusions: P. saltatrix in the south-western Pacific has a growth rate similar to that in other populations of P. saltatrix.
Implications: Despite its geographically and genetically distinct populations, P. saltatrix demonstrates a generally consistent life-history strategy of fast growth and high mortality, except for the north-western Atlantic population, which has lower mortality
- …