12,333 research outputs found
Evidence for nodal superconductivity in LaFePO
In several iron-arsenide superconductors there is strong evidence for a fully
gapped superconducting state consistent with either a conventional s-wave
symmetry or an unusual state where there the gap changes sign between
the electron and hole Fermi surface sheets. Here we report measurements of the
penetration depth in very clean samples of the related
iron-phosphide superconductor, LaFePO, at temperatures down to 100 mK.
We find that varies almost perfectly linearly with strongly
suggesting the presence of gap nodes in this compound. Taken together with
other data, this suggests the gap function may not be generic to all pnictide
superconductors
Rethinking Placental Transfusion and Cord Clamping Issues
A brief delay in clamping the umbilical cord results in a placental transfusion that supplies the infant with a major source of iron during the first few months of life. Cord circulation continues for several minutes after birth and placental transfusion results in approximately 30% more blood volume. Gravity influences the amount of placental transfusion that an infant receives. Placing the infant skin-to-skin requires a longer delay of cord clamping (DCC) than current recommendations. Uterotonics are not contraindicated with DCC. Cord milking is a safe alternative to DCC when one must cut the cord prematurely. Recent randomized controlled trials demonstrate benefits for term and preterm infants from DCC. The belief that DCC causes hyperbilirubinemia or symptomatic polycythemia is unsupported by the available research. Delay of cord clamping substantively increases iron stores in early infancy. Inadequate iron stores in infancy may have an irreversible impact on the developing brain despite oral iron supplementation. Iron deficiency in infancy can lead to neurologic issues in older children including poor school performance, decreased cognitive abilities, and behavioral problems. The management of the umbilical cord in complex situations is inconsistent between birth settings. A change in practice requires collaboration between all types of providers who attend births
Uncovering Bugs in Distributed Storage Systems during Testing (not in Production!)
Testing distributed systems is challenging due to multiple sources of nondeterminism. Conventional testing techniques, such as unit, integration and stress testing, are ineffective in preventing serious but subtle bugs from reaching production. Formal techniques, such as TLA+, can only verify high-level specifications of systems at the level of logic-based models, and fall short of checking the actual executable code. In this paper, we present a new methodology for testing distributed systems. Our approach applies advanced systematic testing techniques to thoroughly check that the executable code adheres to its high-level specifications, which significantly improves coverage of important system behaviors. Our methodology has been applied to three distributed storage systems in the Microsoft Azure cloud computing platform. In the process, numerous bugs were identified, reproduced, confirmed and fixed. These bugs required a subtle combination of concurrency and failures, making them extremely difficult to find with conventional testing techniques. An important advantage of our approach is that a bug is uncovered in a small setting and witnessed by a full system trace, which dramatically increases the productivity of debugging
A neutron scattering study of the interplay between structure and magnetism in Ba(FeCo)As
Single crystal neutron diffraction is used to investigate the magnetic and
structural phase diagram of the electron doped superconductor
Ba(FeCo)As. Heat capacity and resistivity measurements have
demonstrated that Co doping this system splits the combined antiferromagnetic
and structural transition present in BaFeAs into two distinct
transitions. For =0.025, we find that the upper transition is between the
high-temperature tetragonal and low-temperature orthorhombic structures with
( K) and the antiferromagnetic transition occurs at
K. We find that doping rapidly suppresses the
antiferromagnetism, with antiferromagnetic order disappearing at . However, there is a region of co-existence of antiferromagnetism and
superconductivity. The effect of the antiferromagnetic transition can be seen
in the temperature dependence of the structural Bragg peaks from both neutron
scattering and x-ray diffraction. We infer from this that there is strong
coupling between the antiferromagnetism and the crystal lattice
Ladders for Wilson Loops Beyond Leading Order
We set up a general scheme to resum ladder diagrams for the quark-anti-quark
potential in N=4 super-Yang-Mills theory, and do explicit calculations at the
next-to-leading order. The results perfectly agree with string theory in
AdS(5)xS(5) when continued to strong coupling, in spite of a potential
order-of-limits problem.Comment: 18 pages, 5 figure
China Near Seas Combat Capabilities
The capstone U.S. Defense Department study on the future operational environment declares, China\u27s rise represents the most significant single event on the international horizon since the collapse of the Cold War. Understanding and assessing changes in China\u27s traditionally defensive naval strategy, doctrine, and force structure are of obvious importance to the U.S. Navy (USN) and other Pacific navies concerned with the possible security implications of that rise. This chapter examines the development of the Chinese navy\u27s Houbei (Type 022) fast-attack-craft force and its roles and missions in China\u27s near seas and discusses implications for the U.S. Navy and other navies in the region.https://digital-commons.usnwc.edu/cmsi-red-books/1010/thumbnail.jp
Comparing strings in AdS(5)xS(5) to planar diagrams: an example
The correlator of a Wilson loop with a local operator in N=4 SYM theory can
be represented by a string amplitude in AdS(5)xS(5). This amplitude describes
an overlap of the boundary state, which is associated with the loop, with the
string mode, which is dual to the local operator. For chiral primary operators
with a large R charge, the amplitude can be calculated by semiclassical
techniques. We compare the semiclassical string amplitude to the SYM
perturbation theory and find an exact agrement to the first two non-vanishing
orders.Comment: 16 pages, 4 figures, LaTeX; v2: typos corrected; v3: clarification of
boundary conditions at infinity adde
Cardiac asystole at birth: Is hypovolemic shock the cause?
A birth involving shoulder dystocia can rapidly deteriorate—from a fetus with a reassuring tracing in the minutes before birth, to a neonate needing aggressive resuscitation. Infants experiencing a traumatic birth involving shoulder dystocia may be severely compromised, even when the preceding labor was uncomplicated. This paper presents two cases in which infants had normal heart beats recorded 5–10 min before birth and were born with cardiac asystole following shoulder dystocia. Often, in cases of shoulder dystocia, infants shift blood to the placenta due to the tight compressive squeeze of the body in the birth canal (along with cord compression) and thereby may be born hypovolemic. Our hypothesis is that the occurrence of sudden cardiac asystole at birth is due to extreme hypovolemic shock secondary to the loss of blood. At birth, the sudden release of pressure on the infant’s body results in hypoperfusion resulting in low central circulation and blood pressure. Severe hypovolemic shock from these effects leads to sudden cardiac arrest. Immediate cord clamping maintains the hypovolemic state by preventing the physiologic and readily available placental blood from returning to the infant. Loss of this blood initiates an inflammatory response leading to seizures, hypoxic-ischemic encephalopathy, and brain damage or death. Animal studies have shown that human umbilical stem cells injected into a rat’s abdomen after induced brain damage, can protect the rat’s brain from developing permanent injury. To prevent damage to newborns, the infant must receive the blood volume and stem cells lost at the time of descent and immediate cord clamping. Recommended countermeasures for research include: (1) resuscitation at the perineum with intact cord; or (2) milking the cord before clamping; or (3) autologous transfusion of placenta blood after the birth; or (4) rapid transfusion of O negative blood after birth and before seizures begin
Ferromagnetism in the Mott insulator Ba2NaOsO6
Results are presented of single crystal structural, thermodynamic, and
reflectivity measurements of the double-perovskite Ba2NaOsO6. These
characterize the material as a 5d^1 ferromagnetic Mott insulator with an
ordered moment of ~0.2 Bohr magnetons per formula unit and TC = 6.8(3) K. The
magnetic entropy associated with this phase transition is close to Rln2,
indicating that the quartet groundstate anticipated from consideration of the
crystal structure is split, consistent with a scenario in which the
ferromagnetism is associated with orbital ordering.Comment: 5 pages, 5 figures, added reference
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