2,575 research outputs found
Violations of universality in a vectorlike extension of the standard model
Violations of universality of couplings in a vectorlike extension of the
standard model with three heavy mirror fermion families are considered. The
recently observed discrepancies between experiments and the standard model in
the hadronic branching fractions and of the Z-boson are explained
by the mixing of fermions with their mirror fermion partners.Comment: latex2e, 11 page
Posterior lumbar interbody fusion using non resorbable poly-ether-ether-ketone versus resorbable poly-l-lactide-co-d,l-lactide fusion devices. Clinical outcome at a minimum of 2-year follow-up
Previous papers on resorbable poly-l-lactide-co-d,l-lactide (PLDLLA) cages in spinal fusion have failed to report adequately on patient-centred clinical outcome measures. Also comparison of PLDLLA cage with a traditionally applicable counterpart has not been previously reported. This is the first randomized prospective study that assesses clinical outcome of PLDLLA cage compared with a poly-ether-ether-ketone (PEEK) implant. Twenty-six patients were randomly assigned to undergo instrumented posterior lumbar interbody fusion (PLIF) whereby either a PEEK cage or a PLDLLA cage was implanted. Clinical outcome based on visual analogue scale scores for leg pain and back pain, as well as Oswestry Disability Index (ODI) and SF-36 questionnaires were documented and analysed. When compared with preoperative values, all clinical parameters have significantly improved in the PEEK group at 2 years after surgery with the exception of SF-36 general health, SF-36 mental health and SF-36 role emotional scores. No clinical parameter showed significant improvement at 2 years after surgery compared with preoperative values in the PLDLLA patient group. Only six patients (50%) in the PLDLLA group showed improvement in the VAS scores for leg and back pain as well as the ODI, as opposed to 10 patients (71%) in the PEEK group. One-third of the patients in the PLDLLA group actually reported worsening of their pain scores and ODI. Three cases of mild to moderate osteolysis were seen in the PLDLLA group. Following up on our preliminary report, these 2-year results confirm the superiority of the PEEK implant to the resorbable PLDLLA implant in aiding spinal fusion and alleviating symptoms following PLIF in patients with degenerative spondylolisthesis associated with either canal stenosis or foramen stenosis or both and emanating from a single lumbar segment
Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments
We fabricate and characterize carbon-fiber tips for their use in combined
scanning tunneling and force microscopy based on piezoelectric quartz tuning
fork force sensors. An electrochemical fabrication procedure to etch the tips
is used to yield reproducible sub-100-nm apex. We also study electron transport
through single-molecule junctions formed by a single octanethiol molecule
bonded by the thiol anchoring group to a gold electrode and linked to a carbon
tip by the methyl group. We observe the presence of conductance plateaus during
the stretching of the molecular bridge, which is the signature of the formation
of a molecular junction.Comment: Conference Proceeding (Trends in NanoTechnology 2011, Tenerife
SPAIN); Nanoscale Research Letters, (2012) 7:25
Low-lying Eigenvalues of the QCD Dirac Operator at Finite Temperature
We compute the low-lying spectrum of the staggered Dirac operator above and
below the finite temperature phase transition in both quenched QCD and in
dynamical four flavor QCD. In both cases we find, in the high temperature
phase, a density with close to square root behavior, . In the quenched simulations we find, in addition, a
volume independent tail of small eigenvalues extending down to zero. In the
dynamical simulations we also find a tail, decreasing with decreasing mass, at
the small end of the spectrum. However, the tail falls off quite quickly and
does not seem to extend to zero at these couplings. We find that the
distribution of the smallest Dirac operator eigenvalues provides an efficient
observable for an accurate determination of the location of the chiral phase
transition, as first suggested by Jackson and Verbaarschot.Comment: LaTeX, 20 pages, 13 postscript figures. Reference added. To appear in
Nucl. Phys.
Substellar and low-mass dwarf identification with near-infrared imaging space observatories
AIMS: We aim to evaluate the near-infrared colors of brown dwarfs as observed
with four major infrared imaging space observatories: the Hubble Space
Telescope (HST), the James Webb Space Telescope (JWST), the Euclid mission, and
the WFIRST telescope.
METHODS: We used the SPLAT SPEX/ISPEX spectroscopic library to map out the
colors of the M-, L-, and T-type dwarfs. We have identified which color-color
combination is optimal for identifying broad type and which single color is
optimal to then identify the subtype (e.g., T0-9). We evaluated each
observatory separately as well as the narrow-field (HST and JWST) and
wide-field (Euclid and WFIRST) combinations.
RESULTS: The Euclid filters perform poorly typing brown dwarfs and WFIRST
performs only marginally better, despite a wider selection of filters. WFIRST's
W146 and F062 combined with Euclid's Y-band discriminates somewhat better
between broad brown dwarf categories. However, subtyping with any combination
of Euclid and WFIRST observations remains uncertain due to the lack of medium
or narrow-band filters. We argue that a medium band added to the WFIRST filter
selection would greatly improve its ability to preselect brown dwarfs its
imaging surveys.
CONCLUSIONS: The HST filters used in high-redshift searches are close to
optimal to identify broad stellar type. However, the addition of F127M to the
commonly used broad filter sets would allow for unambiguous subtyping. An
improvement over HST is one of two broad and medium filter combinations on
JWST: pairing F140M with either F150W or F162M discriminates very well between
subtypes
Coherent transmission through a one dimensional lattice
Based on the Keldysh nonequilibrium Green function (NGF) technique, a general
formula for the current and transmission coefficient through a one dimensional
lattice is derived without the consideration of electron-electron interactions.
We obtain an analytical condition for perfect resonant transmission when the
levels of sites are aligned, which depends on the parity of the number of
sites. Localization-delocalization transition in a generic one dimensional
disordered lattice is also analyzed, depending on the correlation among the
hopping parameters and the strength of the coupling to reservoirs. The
dependence of the number and lineshape of resonant transmission and linear
conductance peaks on the structure parameters of the lattice is also given in
several site cases.Comment: 22 pages, 3 figures, Revtex, minor revision mad
Does Increased Arterial Stiffness Increase the Risk for Postural Hypotension?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75516/1/j.1076-7460.2005.04503.x.pd
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