Quantum tunneling time

A simple model of a quantum clock is applied to the old and controversial problem of how long a particle takes to tunnel through a quantum barrier. The model I employ has the advantage of yielding sensible results for energy eigenstates, and does not require the use of time-dependant wave packets. Although the treatment does not forbid superluminal tunneling velocities, there is no implication of faster-than-light signaling because only the transit duration is measurable, not the absolute time of transit. A comparison is given with the weak-measurement post-selection calculations of Steinberg.Comment: 10 pages, no figures, research pape

Skin friction coefficient on a yarn package surface in ring spinning

The skin friction coefficient on the surface of a rotating yarn package affects the power required to drive the package. This paper examines the relationship between the skin friction coefficient on the package surface and its diameter and rotating speed, based on the fundamentals of aerodynamics and the experimental results of power consumption. Skin friction coefficients on the surfaces of an airplane, car top, and yarn package are discussed. The results indicate that the skin friction coefficient on the package surface without hairiness depends on the package diameter and spindle speed only. The skin friction coefficient on the yarn package surface is about three times that on the top surface of a car, and is about twenty times that on an airplane surface. The power consumed to overcome skin friction drag is more than that consumed to drive the spindle if the spindle speed is very slow. However, the situation reverses when the spindle speed is fast

Stimulated emission from semi-polar (11-22) GaN overgrown on sapphire

(11-22) semi-polar GaN is expected to exhibit major advantages compared with current c-plane polar GaN in the fabrication of long wavelength such as green and yellow emitters. However, all the III-nitride based semi-/non- polar laser diodes (LDs) reported so far have been achieved exclusively based on homo-epitaxial growth on extremely expensive free-standing GaN substrates with a very limited size. In this paper, we have observed a stimulated emission at room temperature achieved on our semi-polar (11-22) GaN overgrown on a micro-rod arrayed template with an optimized design on m-plane sapphire. This has never been achieved previously on any semi-polar GaN grown on sapphire. Furthermore, an optical gain of 130cm−1 has been measured by means of performing a standard laser stripe-length dependent optical measurement. The values of the threshold and the optical gain obtained are comparable to those of the c-plane GaN reported so far, further validating the satisfactory crystal quality of our overgrown semi-polar (11-22) GaN on sapphire. This represents a major step towards the development of III-nitride semi-polar based LDs on sapphire, especially in the long wavelength regime

ANNOTATED CHECKLIST OF CYRTANDRA (GESNERIACEAE) OF SUMATRA, INDONESIA

WANG, Q. W., BRAMLEY, G. L. C., ATKINS, H. J. & KARTONEGORO, A. 2022. Annotated checklist of Cyrtandra (Gesneriaceae) of Sumatra, Indonesia. Reinwardtia 21(2): 63‒80. — There are 53 species and three varieties of Sumatran Cyrtandra (Gesneriaceae) included in the checklist. Thirty-three lectotypes and four neotypes have been assigned, including for two excluded species. Two species are designated as incertae sedis due to a lack of type material or any associated specimens. A new name of C. jackii is proposed here to replace the illegitimate C. glabra Jack. Most of the species included in the checklist are endemic to Sumatra, with some species distributed in neighboring islands in Malesia. The next step for Cyrtandra in Sumatra is to carry out a full taxonomic revision to better understand distribution patterns and species limits and also to assign appropriate neotypes for those species still missing original material

Use of a T-flex toric intraocular lens to correct clinically significant astigmatism

AbstractPurposeTo investigate the stability and effectiveness of T-flex toric intraocular lenses (IOLs) for the correction of regular corneal astigmatism during cataract surgery.MethodsFrom October 2009 to January 2014 we enrolled patients receiving phacoemulsification and T-flex toric IOL implantation in the capsular bag at the Far Eastern Memorial Hospital. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), corneal astigmatism, refractive astigmatism, and the degree to which the IOL axis deviated from the demanded axis were recorded both before the operation and 6 months postoperatively.ResultsWe enrolled 24 eyes of 24 consecutive patients in this study. The mean spherical power of the implanted toric IOLs was 17.13 ± 4.21 D (range 6.0–24.0 D) and the mean cylindrical power of the IOLs was 3.0 ± 0.86 D (range 2.0–5.0 D). At the 6-month follow up examination, the refractive astigmatism had improved from 3.21 ± 1.50 D to 0.77 ± 0.47 D (p < 0.001) and the spherical equivalence had improved from 4.47 ± 5.43 D to 0.63 ± 0.49 D (p = 0.007). The CDVA improved from 0.81 ± 0.45 logMAR to 0.09 ± 0.11 logMAR (p < 0.001). The mean improvement from the preoperative CDVA to the postoperative UDVA was 5.3 lines on the Snellen chart. Ninety-two percent of our patients achieved a postoperative UDVA ≥20/40 and 67% achieved a postoperative UDVA ≥20/25.ConclusionThe T-flex toric IOL can effectively reduce visually significant corneal astigmatism and improve uncorrected distance visual acuity during cataract surgery

Chemically dealloyed Fe-based metallic glass with void channels-like architecture for highly enhanced peroxymonosulfate activation in catalysis

Metallic glasses (MGs) with their intrinsic disordered atomic structure and widely controllable atomic components have recently emerged as fascinating functional materials in wastewater treatment. Compared to crystalline alloys, the less-noble atomic components in monolithic metallic glass are more efficient to be selectively dissolved during dealloying process. This work reported a facile chemical dealloying approach to fabricate a void channels-like structured MG with the elemental components of Fe73.5Si13.5B9Cu1Nb3 for methylene blue (MB) degradation. Results indicated that the dealloyed Fe73.5Si13.5B9Cu1Nb3 MGs with the void channels-like morphology presented a significant improvement of catalytic efficiency and reusability. The dye degradation reaction rate (kobs) of the dealloyed Fe73.5Si13.5B9Cu1Nb3 MGs presented 3 times higher than their as-spun MGs. More importantly, the dealloyed Fe73.5Si13.5B9Cu1Nb3 MGs can be reused up to 25 times without significantly loosing catalytic efficiency. It was also found that the dealloyed Fe73.5Si13.5B9Cu1Nb3 MGs exhibited a greater corrosion resistance in the simulated dye solution compared to the as-spun ribbons, demonstrating a robust self-healing ability in catalytic activity. This work provides a novel view for designing MG catalysts with high efficiency and stability in worldwide energy and environmental concerns

Cooler Magnetic Spectrometer

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Truth Table Invariant Cylindrical Algebraic Decomposition by Regular Chains

A new algorithm to compute cylindrical algebraic decompositions (CADs) is presented, building on two recent advances. Firstly, the output is truth table invariant (a TTICAD) meaning given formulae have constant truth value on each cell of the decomposition. Secondly, the computation uses regular chains theory to first build a cylindrical decomposition of complex space (CCD) incrementally by polynomial. Significant modification of the regular chains technology was used to achieve the more sophisticated invariance criteria. Experimental results on an implementation in the RegularChains Library for Maple verify that combining these advances gives an algorithm superior to its individual components and competitive with the state of the art

Quasi-Periodic Releases of Streamer Blobs and Velocity Variability of the Slow Solar Wind near the Sun

We search for persistent and quasi-periodic release events of streamer blobs during 2007 with the Large Angle Spectrometric Coronagraph on the \textit{Solar and Heliospheric Observatory} and assess the velocity of the slow solar wind along the plasma sheet above the corresponding streamer by measuring the dynamic parameters of blobs. We find 10 quasi-periodic release events of streamer blobs lasting for three to four days. In each day of these events, we observe three-five blobs. The results are in line with previous studies using data observed near the last solar minimum. Using the measured blob velocity as a proxy for that of the mean flow, we suggest that the velocity of the background slow solar wind near the Sun can vary significantly within a few hours. This provides an observational manifestation of the large velocity variability of the slow solar wind near the Sun.Comment: 14 pages, 5 figures, accepted by Soalr Physic

Experimental and numerical investigation of an air-to-water heat pipe-based heat exchanger

An experimental and analytical investigation was conducted on an air-to-water heat exchanger equipped with six wickless heat pipes (thermosyphons) charged with water as the working fluid. The flow pattern consisted of a double pass on the evaporator and condenser sections. The six thermosyphons were all made from carbon steel, measured 2m in length and were installed in a staggered arrangement. The objectives of the reported experimental investigation were to analyse the effect of multiple air passes at different air inlet temperatures (100 to 250°C) and air mass flow rates (0.05 to 0.14kg/s) on the thermal performance of the heat exchanger unit including the heat pipes. The results were compared with a CFD model that assumed the heat pipes were solid rods with a constant conductivity. The conductivity of the pipes was extracted from modifications of correlations available in the literature based around the theory of Thermal Resistance. The results proved to be very accurate within 10% of the experimental values