4,869 research outputs found
Transmission efficiency limit for nonlocal metalenses
The rapidly advancing capabilities in nanophotonic design are enabling
complex functionalities limited mainly by physical bounds. The efficiency of
transmission is a major consideration, but its ultimate limit remains unknown
for most systems. Here, we introduce a matrix formalism that puts a fundamental
bound on the channel-averaged transmission efficiency of any passive
multi-channel optical system based only on energy conservation and the desired
functionality, independent of the interior structure and material composition.
Applying this formalism to diffraction-limited nonlocal metalenses with a wide
field of view, we show that the transmission efficiency must decrease with the
numerical aperture for the commonly adopted designs with equal entrance and
output aperture diameters. We also show that reducing the size of the entrance
aperture can raise the efficiency bound. This work reveals a fundamental limit
on the transmission efficiency as well as providing guidance for the design of
high-efficiency multi-channel optical systems
Coordinated Multicasting with Opportunistic User Selection in Multicell Wireless Systems
Physical layer multicasting with opportunistic user selection (OUS) is
examined for multicell multi-antenna wireless systems. By adopting a two-layer
encoding scheme, a rate-adaptive channel code is applied in each fading block
to enable successful decoding by a chosen subset of users (which varies over
different blocks) and an application layer erasure code is employed across
multiple blocks to ensure that every user is able to recover the message after
decoding successfully in a sufficient number of blocks. The transmit signal and
code-rate in each block determine opportunistically the subset of users that
are able to successfully decode and can be chosen to maximize the long-term
multicast efficiency. The employment of OUS not only helps avoid
rate-limitations caused by the user with the worst channel, but also helps
coordinate interference among different cells and multicast groups. In this
work, efficient algorithms are proposed for the design of the transmit
covariance matrices, the physical layer code-rates, and the target user subsets
in each block. In the single group scenario, the system parameters are
determined by maximizing the group-rate, defined as the physical layer
code-rate times the fraction of users that can successfully decode in each
block. In the multi-group scenario, the system parameters are determined by
considering a group-rate balancing optimization problem, which is solved by a
successive convex approximation (SCA) approach. To further reduce the feedback
overhead, we also consider the case where only part of the users feed back
their channel vectors in each block and propose a design based on the balancing
of the expected group-rates. In addition to SCA, a sample average approximation
technique is also introduced to handle the probabilistic terms arising in this
problem. The effectiveness of the proposed schemes is demonstrated by computer
simulations.Comment: Accepted by IEEE Transactions on Signal Processin
Identifiability of the Simplex Volume Minimization Criterion for Blind Hyperspectral Unmixing: The No Pure-Pixel Case
In blind hyperspectral unmixing (HU), the pure-pixel assumption is well-known
to be powerful in enabling simple and effective blind HU solutions. However,
the pure-pixel assumption is not always satisfied in an exact sense, especially
for scenarios where pixels are heavily mixed. In the no pure-pixel case, a good
blind HU approach to consider is the minimum volume enclosing simplex (MVES).
Empirical experience has suggested that MVES algorithms can perform well
without pure pixels, although it was not totally clear why this is true from a
theoretical viewpoint. This paper aims to address the latter issue. We develop
an analysis framework wherein the perfect endmember identifiability of MVES is
studied under the noiseless case. We prove that MVES is indeed robust against
lack of pure pixels, as long as the pixels do not get too heavily mixed and too
asymmetrically spread. The theoretical results are verified by numerical
simulations
Performance of CMS ECAL Preshower in 2007 test beam
The Preshower detector is part of the CMS Electromagnetic Calorimeter, located in the endcap regions, in front of the lead tungstate crystals. It consist of two orthogonal planes of silicon strip sensors interleaved with two planes of lead absorbers. A combined beam test of close-to-final prototypes of the Hadron calorimeter, the crystal calorimeter and the Preshower detector was performed in the summer of 2007. Calibrations were made using electron and pion data. The combined crystal and Preshower energy resolution was studied using electrons. Good signal/noise performance was obtained in both sets of measurement
Pentacene-Based Thin-Film Transistors With a Solution-Process Hafnium Oxide Insulator
Abstract—Pentacene-based organic thin-film transistors with
solution-process hafnium oxide (HfOx) as gate insulating layer
have been demonstrated. The solution-process HfOx could not
only exhibit a high-permittivity (κ = 11) dielectric constant but
also has good dielectric strength. Moreover, the root-mean-square
surface roughness and surface energy (γs) on the surface of the
HfOx layer were 1.304 nm and 34.24 mJ/cm2, respectively. The
smooth, as well as hydrophobic, surface of HfOx could facilitate
the direct deposition of the pentacene film without an additional
polymer treatment layer, leading to a high field-effect mobility of
3.8 cm2/(V · s).
Index Terms—Hafnium oxide, high permittivity, organic thinfilm transistor (OTFT), solution process, surface energy
The impact of anti-diabetic drugs on colorectal cancer risk in a large cohort of women with diabetes
No Abstrac
Reward prediction errors arising from switches between major and minor modes in music: An fMRI study
Evidence has accumulated that prediction error processing plays a role in the
enjoyment of music listening. The present study examined listeners' neural
responses to the signed reward prediction errors (RPEs) arising from switches
between major and minor modes in music. We manipulated the final chord of J. S.
Bach's keyboard pieces so that each major-mode passage ended with either the
major (Major-Major) or minor (Major-Minor) tonic chord, and each minor-mode
passage ended with either the minor (Minor-Minor) or major (Minor-Major) tonic
chord. In Western music, the major and minor modes have positive and negative
connotations, respectively. Therefore, the outcome of the final chord in
Major-Minor stimuli was associated with negative RPE, whereas that in
Minor-Major was associated with positive RPE. Twenty-three musically
experienced adults underwent functional magnetic resonance imaging while
listening to Major-Major, Major-Minor, Minor-Minor, and Minor-Major stimuli. We
found that activity in the subgenual anterior cingulate cortex (extending into
the ventromedial prefrontal cortex) during the final chord for Major-Major was
significantly higher than that for Major-Minor. Conversely, a frontoparietal
network for Major-Minor exhibited significantly increased activity compared to
Major-Major. The contrasts between Minor-Minor and Minor-Major yielded regions
implicated in interoception. We discuss our results in relation to executive
functions and the emotional connotations of major versus minor mode.Comment: submitted to Psychophysiolog
Rupture of Renal Pelvis in an Adult with Congenital Ureteropelvic Junction Obstruction After Blunt Abdominal Trauma
Isolated injury to the renal pelvis following blunt abdominal trauma is very rare. However, a pre-existing renal abnormality will increase the risk of rupture. We present a 24-year-old man with rupture of the left renal pelvis following blunt abdominal trauma. He had pre-existing left ureteropelvic junction (UPJ) obstruction. Delayed computed tomography scan with excretory phase revealed contrast medium extravasation from the left UPJ, and left renal pelvis rupture was diagnosed. He was managed successfully with ureteral double-J stenting for 2 months
Effect on Spasticity After Performance of Dynamic-Repeated-Passive Ankle Joint Motion Exercise in Chronic Stroke Patients
Spasticity associated with abnormal muscle tone is a common motor disorder following stroke, and the spastic ankle may affect ambulatory function. The purpose of this study was to investigate the short-term effect of dynamic-repeated-passive ankle movements with weight loading on ambulatory function and spastic hypertonia of chronic stroke patients. In this study, 12 chronic stroke patients with ankle spasticity and inefficient ambulatory ability were enrolled. Stretching of the plantar-flexors of the ankle in the standing position for 15 minutes was performed passively by a constant-speed and electrically powered device. The following evaluations were done before and immediately after the dynamic-repeated-passive ankle movements. Spastic hypertonia was assessed by the Modified Ashworth Scale (MAS; range, 0–4), Achilles tendon reflexes test (DTR; range, 0–4), and ankle clonus (range, 0–5). Improvement in ambulatory ability was determined by the timed up-and-go test (TUG), the 10-minute walking test, and cadence (steps/minute). In addition, subjective experience of the influence of ankle spasticity on ambulation was scored by visual analog scale (VAS). Subjective satisfaction with the therapeutic effect of spasticity reduction was evaluated by a five-point questionnaire (1 = very poor, 2 = poor, 3 = acceptable, 4 = good, 5 = very good). By comparison of the results before and after intervention, these 12 chronic stroke patients presented significant reduction in MAS and VAS for ankle spasticity, the time for TUG and 10-minute walking speed (p < 0.01). The cadence also increased significantly (p < 0.05). In addition, subjective satisfaction with the short-term therapeutic effect was mainly good (ranging from acceptable to very good). In conclusion, 15 minutes of dynamic-repeated-passive ankle joint motion exercise with weight loading in the standing position by this simple constant-speed machine is effective in reducing ankle spasticity and improving ambulatory ability
Comparison of secondary signs as shown by unenhanced helical computed tomography in patients with uric acid or calcium ureteral stones
AbstractUnenhanced helical computed tomography (UHCT) has evolved into a well-accepted diagnostic method in patients with suspected ureterolithiasis. UHCT not only shows stones within the lumen of the ureter, it also permits evaluation of the secondary signs associated with ureteral obstruction from stones. However, there we could find no data on how secondary signs might differ in relation to different compositions of ureteral stones. In this study, we compared the degree of secondary signs revealed by UHCT in uric acid stone formers and in patients forming calcium stones. We enrolled 117 patients with ureteral stones who underwent UHCT examination and Fourier transform infra-red analysis of stone samples. Clinical data were collected as follows: age, sex, estimated glomerular filtration rate (eGFR), urine pH, and radiological data on secondary signs apparent on UHCT. The uric acid stone formers had significantly lower urine pH and eGFR in comparison to calcium stone formers, and on UHCT they also had a higher percentage of the secondary signs, including rim sign (78.9% vs. 60.2%), hydroureter (94.7% vs. 89.8%), perirenal stranding (84.2% vs. 59.2%) and kidney density difference (73.7% vs. 50.0%). The radiological difference was statistically significant for perirenal stranding (p=0.041). In conclusion, we found that UHCT scanning reveals secondary signs to be more frequent in patients with uric acid ureteral stones than in patients with calcium stones, a tendency that might result from an acidic urine environment
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