1,639 research outputs found
Risk factors for ischaemic colitis after surgery for abdominal aortic aneurysm: a systematic review and observational meta-analysis
BACKGROUND: Ischaemic colitis is an infrequent but serious complication following repair of abdominal aortic aneurysm (AAA), with high mortality rates. This systematic review set out to identify risk factors for the development of ischaemic colitis after AAA surgery. METHODS: A systematic search of the MEDLINE, EMBASE and CINAHL databases was performed. This search was limited to studies published in the English language after 1990. Abstracts were screened by two authors. Eligible studies were obtained as full text for further examination. Data was extracted by two authors, and any disputes were resolved via consensus. Extracted data was pooled using Mantel-Haenszel random effects models. Bias was assessed using two Cochrane-approved tools. Effect sizes are expressed as relative risk ratios alongside the 95 % confidence interval. Statistical significance was defined at the level of p < 0.05. RESULTS: From 388 studies identified in the initial search, 33 articles were included in the final synthesis and analysis. Risk factors were grouped into patient (female gender, disease severity) and operative factors (peri-procedural hypotension, operative modality). The risk of ischaemic colitis was significantly higher when undergoing emergency repair versus elective (risk ratio (RR) 7.36, 3.08 to 17.58, p < 0.001). Endovascular repair reduced the likelihood of ischaemic colitis (RR 0.22, 0.12 to 0.39, p < 0.001). DISCUSSION: The quality of published evidence on this subject is poor with many retrospective datasets and inconsistent reporting across studies. Despite this, emergency presentation and open repair should prompt close monitoring for the development of IC
Quantification of volatile flavor compounds in off-flavor and commercial reduced-fat milk samples
Various chemical compounds contribute to the naturally pleasant flavor of milk. Over time, however, and with unwanted chemical reactions, loss of flavor is inevitable. This study was conducted to identify and quantify volatile flavor compounds associated with off-flavored and commercial reduced-fat milk products. Fresh milk was used for the preparation of altered milk samples having off-flavors such as light-oxidized and high-acid. Milk lacking freshness (i.e., milk produced two weeks before sampling and maintained at 40oF in the dark) also was compared with fresh unaltered milk and two commercial milk samples. For headspace analysis, milk samples were subjected to SPME-GC for volatile compound identification. In addition, the composition and aerobic and coliform microbial counts for all milk samples were analyzed. The milk samples did not differ in the concentrations of volatile flavor constituents. When comparing light-oxidized milk samples (200 lx exposure for 1 or 3 hr), 2-butanone and pentanal concentrations tended to increase as light exposure time increased. All milk samples had similar fat and total solids contents. High-acid milk had a greater total aerobic microbe count than the other milk samples. Fresh milk had a greater octanal concentration than the offflavored reduced-fat milk samples did. This might indicate that octanal is an important contributor to fresh milk flavor and deserves further study.; Dairy Day, 2004, Kansas State University, Manhattan, KS, 2004
Spin-triplet superconductivity in repulsive Hubbard models with disconnected Fermi surfaces: a case study on triangular and honeycomb lattices
We propose that spin-fluctuation-mediated spin-triplet superconductivity may
be realized in repulsive Hubbard models with disconnected Fermi surfaces. The
idea is confirmed for Hubbard models on triangular (dilute band filling) and
honeycomb (near half-filling) lattices using fluctuation exchange
approximation, where triplet pairing order parameter with f-wave symmetry is
obtained. Possible relevance to real superconductors is suggested.Comment: 5 pages, 6 figures, RevTeX, uses epsf.sty and multicol.st
Tomography of pairing symmetry from magnetotunneling spectroscopy -- a case study for quasi-1D organic superconductors
We propose that anisotropic -, -, or -wave pairing symmetries can be
distinguished from a tunneling spectroscopy in the presence of magnetic fields,
which is exemplified here for a model organic superconductor .
The shape of the Fermi surface (quasi-one-dimensional in this example) affects
sensitively the pairing symmetry, which in turn affects the shape (U or V) of
the gap along with the presence/absence of the zero-bias peak in the tunneling
in a subtle manner. Yet, an application of a magnetic field enables us to
identify the symmetry, which is interpreted as an effect of the Doppler shift
in Andreev bound states.Comment: 4 papegs, 4 figure
Metric trees of generalized roundness one
Every finite metric tree has generalized roundness strictly greater than one.
On the other hand, some countable metric trees have generalized roundness
precisely one. The purpose of this paper is to identify some large classes of
countable metric trees that have generalized roundness precisely one.
At the outset we consider spherically symmetric trees endowed with the usual
combinatorial metric (SSTs). Using a simple geometric argument we show how to
determine decent upper bounds on the generalized roundness of finite SSTs that
depend only on the downward degree sequence of the tree in question. By
considering limits it follows that if the downward degree sequence of a SST satisfies , then has generalized roundness one. Included among the
trees that satisfy this condition are all complete -ary trees of depth
(), all -regular trees () and inductive limits
of Cantor trees.
The remainder of the paper deals with two classes of countable metric trees
of generalized roundness one whose members are not, in general, spherically
symmetric. The first such class of trees are merely required to spread out at a
sufficient rate (with a restriction on the number of leaves) and the second
such class of trees resemble infinite combs.Comment: 14 pages, 2 figures, 2 table
Coexistence or Separation of the Superconducting, Antiferromagnetic, and Paramagnetic Phases in Quasi One-Dimensional (TMTSF)2PF6 ?
We report on experimental studies of the character of phase transitions in
the quasi-1D organic compound (TMTSF)2PF6 in the close vicinity of the borders
between the paramagnetic metal PM, antiferromagnetic insulator AF, and
superconducting SC states. In order to drive the system through the phase
border P_0(T_0), the sample was maintained at fixed temperature T and pressure
P, whereas the critical pressure P_0 was tuned by applying the magnetic field
B. In this approach, the magnetic field was used (i) for tuning (P-P_0), and
(ii) for identifying the phase composition (due to qualitatively different
magnetoresistance behavior in different phases). Experimentally, we measured
R(B) and its temperature dependence R(B,T) in the pressure range (0 - 1)GPa.
Our studies focus on the features of the magnetoresistance at the phase
transition between the PM and AF phases, in the close vicinity to the
superconducting transition at T~1K. We found pronounced history effects arising
when the AF/PM phase border is crossed by sweeping the magnetic field: the
resistance depends on a trajectory which the system arrives at a given point of
the P-B-T phase space. In the transition from the PM to AF phase, the features
of the PM phase extends well into the AF phase. At the opposite transition from
the AF to PM phase, the features of the AF phase are observed in the PM phase.
These results evidence for a macroscopically inhomogeneous state, which
contains macroscopic inclusions of the minority phase. When the system is
driven away from the transition, the homogeneous state is restored; upon a
return motion to the phase boundary, no signatures of the minority phase are
observed up to the very phase boundary.Comment: 10 figures, 23 page
Conductivity Due to Classical Phase Fluctuations in a Model For High-T_c Superconductors
We consider the real part of the conductivity, \sigma_1(\omega), arising from
classical phase fluctuations in a model for high-T_c superconductors. We show
that the frequency integral of that conductivity, \int_0^\infty \sigma_1
d\omega, is non-zero below the superconducting transition temperature ,
provided there is some quenched disorder in the system. Furthermore, for a
fixed amount of quenched disorder, this integral at low temperatures is
proportional to the zero-temperature superfluid density, in agreement with
experiment. We calculate \sigma_1(\omega) explicitly for a model of overdamped
phase fluctuations.Comment: 4pages, 2figures, submitted to Phys.Rev.
Unconventional spin density wave in (TMTSF)2PF6 below T* ~ 4K
The presence of subphases in spin-density wave (SDW) phase of (TMTSF)2PF6
below T* ~ 4K has been suggested by several experiments but the nature of the
new phase is still controversial. We have investigated the temperature
dependence of the angular dependence of the magnetoresistance in the SDW phase
which shows different features for temperatures above and below T*. For T > 4K
the magnetoresistance can be understood in terms of the Landau quantization of
the quasiparticle spectrum in a magnetic field, where the imperfect nesting
plays the crucial role. We propose that below T* ~ 4K the new unconventional
SDW (USDW) appears modifying dramatically the quasiparticle spectrum. Unlike
conventional SDW the order parameter of USDW depends on the quasiparticle
momentum. The present model describes many features of the angular dependence
of magnetoresistance reasonably well. Therefore, we may conclude that the
subphase in (TMTSF)2PF6 below T* ~ 4K is described as SDW plus USDW.Comment: 7 pages, 9 figures, RevTeX4; misprint corrected, references updated,
a few sentences adde
Periodic orbit resonances in layered metals in tilted magnetic fields
The frequency dependence of the interlayer conductivity of a layered Fermi
liquid in a magnetic field which is tilted away from the normal to the layers
is considered. For both quasi-one- and quasi-two-dimensional systems resonances
occur when the frequency is a harmonic of the frequency at which the magnetic
field causes the electrons to oscillate on the Fermi surface within the layers.
The intensity of the different harmonic resonances varies significantly with
the direction of the field. The resonances occur for both coherent and weakly
incoherent interlayer transport and so their observation does not imply the
existence of a three-dimensional Fermi surface.Comment: 4 pages, RevTeX + epsf, 2 figures. Discussion of other work revised.
To appear in Phys. Rev. B, Rapid Commun., October 1
Solidification behavior of intensively sheared hypoeutectic Al-Si alloy liquid
The official published version of this article can be found at the link below.The effect of the processing temperature on the microstructural and mechanical properties of Al-Si (hypoeutectic) alloy solidified from intensively sheared liquid metal has been investigated systematically. Intensive shearing gives a significant refinement in grain size and intermetallic particle size. It also is observed that the morphology of intermetallics, defect bands, and microscopic defects in high-pressure die cast components are affected by intensive shearing the liquid metal. We attempt to discuss the possible mechanism for these effects.Funded by the EPSRC
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