9,087 research outputs found
Quantum Hall line junction with impurities as a multi-slit Luttinger liquid interferometer
We report on quantum interference between a pair of counterpropagating
quantum Hall edge states that are separated by a high quality tunnel barrier.
Observed Aharonov-Bohm oscillations are analyzed in terms of resonant tunneling
between coupled Luttinger liquids that creates bound electronic states between
pairs of tunnel centers that act like interference slits. We place a lower
bound in the range of 20-40 m for the phase coherence length and directly
confirm the extended phase coherence of quantum Hall edge states.Comment: 4 pages, 3 figures, 1 tabl
Prototype laser-diode-pumped solid state laser transmitters
Monolithic, diode-pumped Nd:YAG ring lasers can provide diffraction-limited, single-frequency, narrow-linewidth, tunable output which is adequate for use as a local oscillator in a coherent communication system. A laser was built which had a linewidth of about 2 kHz, a power of 5 milliwatts, and which was tunable over a range of 30 MHz in a few microseconds. This laser was phase-locked to a second, similar laser. This demonstrates that the powerful technique of heterodyne detection is possible with a diode-pumped laser used as the local oscillator. Laser diode pumping of monolithic Nd:YAG rings can lead to output powers of hundreds of milliwatts from a single laser. A laser was built with a single-mode output of 310 mW. Several lasers can be chained together to sum their power, while maintaining diffraction-limited, single frequency operation. This technique was demonstrated with two lasers, with a total output of 340 mW, and is expected to be practical for up to about ten lasers. Thus with lasers of 310 mW, output of up to 3 W is possible. The chaining technique, if properly engineered, results in redundancy. The technique of resonant external modulation and doubling is designed to efficiently convert the continuous wave, infrared output of our lasers into low duty-cycle pulsed green output. This technique was verified through both computer modeling and experimentation. Further work would be necessary to develop a deliverable system using this technique
Revised Orbit and Transit Exclusion for HD 114762b
Transiting planets around bright stars have allowed the detailed follow-up
and characterization of exoplanets, such as the study of exoplanetary
atmospheres. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) is
refining the orbits of the known exoplanets to confirm or rule out both transit
signatures and the presence of additional companions. Here we present results
for the companion orbiting HD 114762 in an eccentric 84 day orbit. Radial
velocity analysis performed on 19 years of Lick Observatory data constrain the
uncertainty in the predicted time of mid-transit to ~5 hours, which is less
than the predicted one-half day transit duration. We find no evidence of
additional companions in this system. New photometric observations with one of
our Automated Photoelectric Telescopes (APTs) at Fairborn Observatory taken
during a revised transit time for companion b, along with 23 years of nightly
automated observations, allow us to rule out on-time central transits to a
limit of ~0.001 mag. Early or late central transits are ruled out to a limit of
~0.002 mag, and transits with half the duration of a central transit are ruled
out to a limit of ~0.003 mag.Comment: 5 pages, 2 figures, accepted for publication in ApJ
Hall-effect and resistivity measurements in CdTe and ZnTe at high pressure: Electronic structure of impurities in the zincblende phase and the semi-metallic or metallic character of the high-pressure phases
We carried out high-pressure resistivity and Hall-effect measurements in
single crystals of CdTe and ZnTe up to 12 GPa. Slight changes of transport
parameters in the zincblende phase of CdTe are consitent with the shallow
character of donor impurities. Drastic changes in all the transport parameters
of CdTe were found around 4 GPa, i.e. close to the onset of the cinnabar to
rock-salt transition. In particular, the carrier concentration increases by
more than five orders of magnitude. Additionally, an abrupt decrease of the
resistivity was detected around 10 GPa. These results are discussed in
comparison with optical, thermoelectric, and x-ray diffraction experiments. The
metallic character of the Cmcm phase of CdTe is confirmed and a semi-metallic
character is determined for the rock-salt phase. In zincblende ZnTe, the
increase of the hole concentration by more than two orders of magnitude is
proposed to be due to a deep-to-shallow transformation of the acceptor levels.
Between 9 and 11 GPa, transport parameters are consistent with the
semiconducting character of cinnabar ZnTe. A two orders of magnitude decrease
of the resistivity and a carrier-type inversion occurs at 11 GPa, in agreement
with the onset of the transition to the Cmcm phase of ZnTe. A metallic
character for this phase is deduced.Comment: 20 pages, 4 figure
Integer quantum Hall effect on a six valley hydrogen-passivated silicon (111) surface
We report magneto-transport studies of a two-dimensional electron system
formed in an inversion layer at the interface between a hydrogen-passivated
Si(111) surface and vacuum. Measurements in the integer quantum Hall regime
demonstrate the expected sixfold valley degeneracy for these surfaces is
broken, resulting in an unequal occupation of the six valleys and anisotropy in
the resistance. We hypothesize the misorientation of Si surface breaks the
valley states into three unequally spaced pairs, but the observation of odd
filling factors, is difficult to reconcile with non-interacting electron
theory.Comment: 4 pages, 4 figures, to appear in Physical Review Letter
Dichotomous development of the gut microbiome in preterm infants.
BackgroundPreterm infants are at risk of developing intestinal dysbiosis with an increased proportion of Gammaproteobacteria. In this study, we sought the clinical determinants of the relative abundance of feces-associated Gammaproteobacteria in very low birth weight (VLBW) infants. Fecal microbiome was characterized at ≤ 2 weeks and during the 3rd and 4th weeks after birth, by 16S rRNA amplicon sequencing. Maternal and infant clinical characteristics were extracted from electronic medical records. Data were analyzed by linear mixed modeling and linear regression.ResultsClinical data and fecal microbiome profiles of 45 VLBW infants (gestational age 27.9 ± 2.2 weeks; birth weight 1126 ± 208 g) were studied. Three stool samples were analyzed for each infant at mean postnatal ages of 9.9 ± 3, 20.7 ± 4.1, and 29.4 ± 4.9 days. The average relative abundance of Gammaproteobacteria was 42.5% (0-90%) at ≤ 2 weeks, 69.7% (29.9-86.9%) in the 3rd, and 75.5% (54.5-86%) in the 4th week (p < 0.001). Hierarchical and K-means clustering identified two distinct subgroups: cluster 1 started with comparatively low abundance that increased with time, whereas cluster 2 began with a greater abundance at ≤ 2 weeks (p < 0.001) that decreased over time. Both groups resembled each other by the 3rd week. Single variants of Klebsiella and Staphylococcus described variance in community structure between clusters and were shared between all infants, suggesting a common, hospital-derived source. Fecal Gammaproteobacteria was positively associated with vaginal delivery and antenatal steroids.ConclusionsWe detected a dichotomy in gut microbiome assembly in preterm infants: some preterm infants started with low relative gammaproteobacterial abundance in stool that increased as a function of postnatal age, whereas others began with and maintained high abundance. Vaginal birth and antenatal steroids were identified as predictors of Gammaproteobacteria abundance in the early (≤ 2 weeks) and later (3rd and 4th weeks) stool samples, respectively. These findings are important in understanding the development of the gut microbiome in premature infants
The HD 192263 system: planetary orbital period and stellar variability disentangled
As part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS), we
present new radial velocities and photometry of the HD 192263 system. Our
analysis of the already available Keck-HIRES and CORALIE radial velocity
measurements together with the five new Keck measurements we report in this
paper results in improved orbital parameters for the system. We derive
constraints on the size and phase location of the transit window for HD
192263b, a Jupiter-mass planet with a period of 24.3587 \pm 0.0022 days. We use
10 years of Automated Photoelectric Telescope (APT) photometry to analyze the
stellar variability and search for planetary transits. We find continuing
evidence of spot activity with periods near 23.4 days. The shape of the
corresponding photometric variations changes over time, giving rise to not one
but several Fourier peaks near this value. However, none of these frequencies
coincides with the planet's orbital period and thus we find no evidence of
star-planet interactions in the system. We attribute the ~23-day variability to
stellar rotation. There are also indications of spot variations on longer (8
years) timescales. Finally, we use the photometric data to exclude transits for
a planet with the predicted radius of 1.09 RJ, and as small as 0.79 RJ.Comment: 9 pages, 6 tables, 6 figures; accepted to Ap
Spin Injection into a Luttinger Liquid
We study the effect of spin injection into a Luttinger liquid. The
spin-injection-detection setup of Johnson and Silsbee is considered; here spins
injected into the Luttinger liquid induce, across an interface with a
ferromagnetic metal, either a spin-dependent current () or a
spin-dependent boundary voltage (). We find that the spin-charge
separation nature of the Luttinger liquid affects and in a very
different fashion. In particular, in the Ohmic regime, depends on the
spin transport properties of the Luttinger liquid in essentially the same way
as it would in the case of a Fermi liquid. The implications of our results for
the spin-injection-detection experiments in the high cuprates are
discussed.Comment: 4 pages, REVTEX, 2 figures. Minor changes and corrections to typos.
To appear in Phys. Rev. Let
Platelet-Rich Plasma Injection With Percutaneous Needling for Recalcitrant Lateral Epicondylitis: Comparison of Tenotomy and Fenestration Techniques.
Background: Recalcitrant lateral epicondylitis (LE) is a common debilitating condition, with numerous treatment options of varying success. An injection of platelet-rich plasma (PRP) has been shown to improve LE, although it is unclear whether the method of needling used in conjunction with a PRP injection is of clinical importance.
Purpose: To determine whether percutaneous needle tenotomy is superior to percutaneous needle fenestration when each is combined with a PRP injection for the treatment of recalcitrant LE.
Study Design: Cohort study; Level of evidence, 3.
Methods: A total of 93 patients with recalcitrant LE were treated with a PRP injection and percutaneous needle fenestration (n = 45) or percutaneous needle tenotomy (n = 48) over a 5-year study interval. Preoperative patient data, including visual analog scale for pain (VAS-P), Quick Disabilities of the Arm, Shoulder and Hand (QuickDASH), and Patient-Rated Tennis Elbow Evaluation (PRTEE) scores and grip strength, were obtained from a chart review and compared with postoperative values obtained prospectively. Secondary outcomes included the incidence of complications, need for additional interventions, return to work, and patient satisfaction.
Results: At a mean follow-up of 40 months, significant improvements in VAS-P (mean, -6.1; 95% CI, -6.8 to -5.5; P \u3c .0001), QuickDASH (mean, -46; 95% CI, -52 to -40; P \u3c .0001), and PRTEE (mean, -57; 95% CI, -64 to -50; P \u3c .0001) scores and grip strength (mean, +6.1 kg; 95% CI, 4.9 to 7.3; P \u3c .0001) were observed across the entire study cohort, with no significant differences noted between the fenestration and tenotomy groups. Nine of 45 patients (22%) underwent additional procedures to treat recurrent symptoms in the fenestration group compared with 5 of 48 patients (10%) in the tenotomy group (P = .05). No complications occurred in any patients, and no patients expressed dissatisfaction with their treatment course.
Conclusion: A PRP injection with concomitant percutaneous needling is an effective treatment for recalcitrant LE, with sustained improvements in pain, strength, and function demonstrated at a mean follow-up of longer than 3 years. Although the method of concomitant needling does not appear to have a significant effect on treatment outcomes, more aggressive needle tenotomy is less likely to require conversion to open tenotomy than needle fenestration in the short term to midterm
Refined Properties of the HD 130322 Planetary System
Exoplanetary systems closest to the Sun, with the brightest host stars,
provide the most favorable opportunities for characterization studies of the
host star and their planet(s). The Transit Ephemeris Refinement and Monitoring
Survey uses both new radial velocity measurements and photometry in order to
greatly improve planetary orbit uncertainties and the fundamental properties of
the star, in this case HD 130322. The only companion, HD 130322b, orbits in a
relatively circular orbit, e = 0.029 every ~10.7 days. Radial velocity
measurements from multiple sources, including 12 unpublished from the Keck I
telescope, over the course of ~14 years have reduced the uncertainty in the
transit midpoint to ~2 hours. The transit probability for the b-companion is
4.7%, where M_p sin i = 1.15 M_J and a = 0.0925 AU. In this paper, we compile
photometric data from the T11 0.8m Automated Photoelectric Telescope at
Fairborn Observatory taken over ~14 years, including the constrained transit
window, which results in a dispositive null result for both full transit
exclusion of HD 130322b to a depth of 0.017 mag and grazing transit exclusion
to a depth of ~0.001 mag. Our analysis of the starspot activity via the
photometric data reveals a highly accurate stellar rotation period: 26.53
+/-0.70 days. In addition, the brightness of the host with respect to the
comparison stars is anti-correlated with the Ca II H and K indices, typical for
a young solar-type star.Comment: 9 pages, 4 figures, 4 tables, accepted to Ap
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