bluuebunny/crossref_metadata_2025 huggingface dataset:
A static‐commutated device to contain voltage variations for low‐voltage active users
Authors: Casolino Giovanni Mercurio , Di Nitto Biagio , Russo Mario
Published: May 2021

The ever‐wider spread of distributed generation in distribution systems feeds the increasing demand for voltage regulation in low‐voltage networks. For these distribution grids, characterised by simpler structures than medium voltage systems but with a larger number of buses and feeders, voltage control devices have to guarantee fast and reliable operation, as well as economic and simple implementation. A key issue is ensuring adequate voltage amplitude for the active users, which present both load and generation. Variations of active power injections/absorptions by active users can produce long‐duration variations of the voltage amplitudes that exceed normal operating ranges admitted for the feeders, thus causing distributed generation tripping and poor power quality for the loads. This work is intended as ‘concept proof' to demonstrate the possibility of obtaining a simple, compact, and cheap device that guarantees adequate voltage amplitudes at low‐voltage user's premises. The device consists of a transformer that can vary its winding arrangements using controlled static switches. A summary of the construction aspects is recalled focussing attention on the control logic and operating characteristics. Various laboratory tests on a prototype are reported, under various operating conditions, highlighting the pros and cons of the considered solution and the margins of improvement.
Highly Concentrated Autologous Platelet-Rich Plasma Restores Foveal Anatomy in Lamellar Macular Hole Surgery
Authors: Hagenau Felix , Nobl Matthias , Vogt Denise , Schworm Benedikt , Siedlecki Jakob , Kreutzer Thomas , Luft Nikolaus , Priglinger Siegfried
Published: May 2021

Background Lamellar macular holes (LMHs) are an entity of a progressive disease in which the efficacy of the therapy of choice, vitrectomy, seems to be reduced. It is unknown whether highly concentrated autologous platelet-rich plasma (PRP) is of value in the therapy of LMHs. The purpose of this study was to gauge the potential of highly concentrated PRP to restore foveal anatomy in LMH surgery.

Patients and Methods In this interventional case series, eight eyes of eight patients with progressive LMH were included. All patients underwent a 23-gauge pars plana vitrectomy with induction of a posterior vitreous detachment and peeling of tractive epiretinal membranes whenever present. Under air tamponade, 0.1 mL of highly concentrated autologous PRP was applied. Subsequently, a gas or air tamponade was performed. All patients were instructed to rest in the supine position for the first 1 to 2 postoperative hours. Best-corrected visual acuity (BCVA) testing, microperimetry, spectral-domain optical coherence tomography (SD-OCT) and fundus photography were performed prior to and 3 months after surgery.

Results SD-OCT showed closure of the macular defect with restoration of a normal foveal configuration in all (8 of 8) patients 3 months postoperatively. BCVA improved significantly, from 0.28 ± 0.08 to 0.12 ± 0.14 logMAR (Wilcoxon: p = 0.03). Microperimetry remained unchanged (24.13 ± 1.96 vs. 23.7 ± 1.54 dB; p = 0.46). No clinically significant intra- or postoperative complications were observed.

Conclusion The use of highly concentrated PRP enables excellent anatomical and functional outcomes in the surgical therapy of LMH. Further prospective comparative trials are warranted to compare this promising technique with existing surgical strategies.
Vitamin B12 and Folate as Risk Factors for Retinal Vein Occlusion: A Meta-Analysis
Authors: Kazantzis Dimitrios , Theodossiadis Panagiotis , Kroupis Christos , Theodossiadis George , Chatziralli Irini
Published: May 2021

Purpose To evaluate the association between serum vitamin B12/folate and retinal vein occlusion (RVO).

Methods A comprehensive search of the PubMed database was performed, which identified 271 abstracts to be screened. Ten studies met our inclusion criteria and a meta-analysis of these comparative case-control studies was performed on the mean ± standard deviation serum vitamin B12 and folate levels, without language restrictions. Nine studies with 720 patients with RVO and 613 controls were included in the meta-analysis for vitamin B12, and 10 studies with 784 patients with RVO and 677 controls in the meta-analysis for folate.

Results There was no statistically significant difference between patients with RVO and controls in serum vitamin B12 levels (mean difference: − 40.25 pg/mL, p = 0.28), either central RVO (mean difference: − 18.24 pg/mL, p = 0.71) or branch RVO (mean difference: − 23.56 pg/mL, p = 0.48). On the contrary, the plasma folate level was significantly lower in RVO patients than in controls (mean difference: − 1.34 ng/mL, p = 0.001), as well as in patients with CRVO compared to controls (mean difference: − 1.48 ng/mL, p = 0.006), but not in BRVO patients (mean difference: − 0.72 ng/mL, p = 0.11).

Conclusions RVO is associated with low serum folate levels, but not with serum vitamin B12 levels.
Sinonasal Symptom Outcomes following Endoscopic Anterior Cranial Base Surgery in the Pediatric Population
Authors: Carle Taylor R. , Wung Vivian , Heaney Anthony P. , Chiu Harvey K. , Suh Jeffrey D. , Bergsneider Marvin , Wang Marilene B.
Published: May 2021

Objective This study aimed to evaluate the impact of endoscopic anterior cranial base (ACB) surgery on sinonasal symptoms in the pediatric population utilizing the Sino-Nasal Outcome Test (SNOT)-22 questionnaire.

Design This is a retrospective review.

Setting The study was conducted at a tertiary academic medical center.

Participants Thirty-four consecutive patients, age 6 to 17 years, M:F 14:20, who underwent endoscopic ACB surgery from July 2008 to August 2019. Ten patients had baseline and a minimum of two subsequent postoperative SNOT-22 questionnaires available for analysis.

Main Outcome Measures Baseline and postoperative SNOT-22 scores were compared. The mean change from baseline sinonasal symptom scores in the pediatric and historical adult cohorts was compared.

Results The mean baseline SNOT-22 score for our 10 patient cohort was 0.46 out of 5 for each of the first 10 sinonasal-specific questions. This worsened to 1.69 at 1 month and returned to near baseline, 0.7, at 3 months postoperatively. The mean quality-of-life score improved to 0.91 at 1 month and 0.6 at 3 months postoperatively. The mean change from baseline for the following items: need to blow nose, runny nose, postnasal discharge, thick nasal discharge, wake up at night, reduced concentration, and frustrated/restless/irritable were similar to those in our historical adult cohort at 3 months postoperatively.

Conclusion Endoscopic ACB surgery in the pediatric population results in increased sinonasal symptom morbidity in the early postoperative period; however, symptoms return to near baseline by ∼3 months, and quality-of-life scores progressively improve in the postoperative period. These trends were similar to those seen in our historic adult cohort.
Intelligent aging compensation scheme for oven-controlled crystal oscillators of batch production based on statistical distribution
Authors: Miao Miao , Li Zhiqi , Zhang Yi , Feng Nana , Zhou Wei
Published: May 2021

The aging of crystal oscillators is an inherent and irreversible process. There is often thought to be no need for special processing if the aging rate varies within an allowable range and the crystal oscillator works properly. However, the impact of aging can be aggravated over the course of lengthy operation. This paper proposes an intelligent compensation scheme for the aging of batch OCXOs (oven-controlled crystal oscillators) based on a statistical distribution, analyzes the aging data of OCXOs in the same batch, selects the typical samples, acquires the best aging prediction curves after assessing different models, and efficiently compensates for every qualified product for aging using this model. The results of experiments exhibited good compensation effects, with an improvement of one to two orders of magnitude in the aging indicators of the compensated OCXOs compared with the original without compensation.
Immunization of networks with limited knowledge and temporary immunity
Authors: Shang Y.
Published: May 2021

Modern view of network resilience and epidemic spreading has been shaped by percolation tools from statistical physics, where nodes and edges are removed or immunized randomly from a large-scale network. In this paper, we produce a theoretical framework for studying targeted immunization in networks, where only n nodes can be observed at a time with the most connected one among them being immunized and the immunity it has acquired may be lost subject to a decay probability ρ. We examine analytically the percolation properties as well as scaling laws, which uncover distinctive characters for Erdős–Rényi and power-law networks in the two dimensions of n and ρ. We study both the case of a fixed immunity loss rate as well as an asymptotic total loss scenario, paving the way to further understand temporary immunity in complex percolation processes with limited knowledge.
Speed limits of protein assembly with reversible membrane localization
Authors: Mishra Bhavya , Johnson Margaret E.
Published: May 2021

Protein assembly is often studied in a three-dimensional solution, but a significant fraction of binding events involve proteins that can reversibly bind and diffuse along a two-dimensional surface. In a recent study, we quantified how proteins can exploit the reduced dimensionality of the membrane to trigger complex formation. Here, we derive a single expression for the characteristic timescale of this multi-step assembly process, where the change in dimensionality renders rates and concentrations effectively time-dependent. We find that proteins can accelerate dimer formation due to an increase in relative concentration, driving more frequent collisions, which often win out over slow-downs due to diffusion. Our model contains two protein populations that dimerize with one another and use a distinct site to bind membrane lipids, creating a complex reaction network. However, by identifying two major rate-limiting pathways to reach an equilibrium steady-state, we derive an excellent approximation for the mean first passage time when lipids are in abundant supply. Our theory highlights how the “sticking rate” or effective adsorption coefficient of the membrane is central in controlling timescales. We also derive a corrected localization rate to quantify how the geometry of the system and diffusion can reduce rates of membrane localization. We validate and test our results using kinetic and particle-based reaction-diffusion simulations. Our results establish how the speed of key assembly steps can shift by orders-of-magnitude when membrane localization is possible, which is critical to understanding mechanisms used in cells.
Non-linear effects and electron heating dynamics in radio-frequency capacitively coupled plasmas with a non-uniform transverse magnetic field
Authors: Liu Yue , Trieschmann Jan , Berger Birk , Schulze Julian , Mussenbrock Thomas
Published: May 2021

A non-uniform transverse magnetic field is used to increase the plasma density and create an asymmetry in radio frequency capacitively coupled plasmas for plasma sputtering and plasma vapor deposition. Based on one-dimensional particle-in-cell/Monte Carlo collision simulations, the effect of the magnetic field magnitude on the non-linear behavior and the electron heating dynamics is studied for a pure helium plasma at a pressure of 30 mTorr. The results show that increasing the magnetic field magnitude can generate a more positive DC self-bias. As a result, non-linear oscillations of the electron current density and the electric field close to the grounded electrode are enhanced. An electric field reversal is induced when the powered electrode sheath collapses to balance electron and ion fluxes toward this boundary due to the strong confinement of electrons. Anomalous energetic electron beams are observed propagating from the collapsed sheath toward the plasma bulk. It is shown that such beams are reflections of the beams originating from the opposite expanding sheath based on the analysis of single particle motions. We show that energetic electron beams can be reflected by the transverse magnetic field.
Enhanced extreme ultraviolet high-harmonic generation from chromium-doped magnesium oxide
Authors: Nefedova V. E. , Fröhlich S. , Navarrete F. , Tancogne-Dejean N. , Franz D. , Hamdou A. , Kaassamani S. , Gauthier D. , Nicolas R. , Jargot G. , Hanna M. , Georges P. , Ciappina M. F. , Thumm U. , Boutu W. , Merdji H.
Published: May 2021

High-order harmonic generation (HHG) from crystals is emerging as a new ultrashort source of coherent extreme ultraviolet (XUV) light. Doping the crystal structure can offer a new way to control the source properties. Here, we present a study of HHG enhancement in the XUV spectral region from an ionic crystal, using dopant-induced vacancy defects, driven by a laser centered at a wavelength of 1.55 μm. Our numerical simulations based on solutions of the semiconductor Bloch equations and density-functional theory are supported by our experimental observations and demonstrate an increase in the XUV high harmonic yield from doped bulk magnesium oxide (MgO) compared to undoped MgO, even at a low defect concentration. The anisotropy of the harmonic emission as a function of the laser polarization shows that the pristine crystal's symmetry is preserved. Our study paves the way toward the control of HHG in solids with complex defects caused by transition-metal doping.
Surface thermodynamics at the nanoscale
Authors: Elliott Janet A. W.
Published: May 2021

Fluid interfaces with nanoscale radii of curvature are generating great interest, both for their applications and as tools to probe our fundamental understanding. One important question is what is the smallest radius of curvature at which the three main thermodynamic combined equilibrium equations are valid: the Kelvin equation for the effect of curvature on vapor pressure, the Gibbs–Thomson equation for the curvature-induced freezing point depression, and the Ostwald–Freundlich equation for the curvature-induced increase in solubility. The objective of this Perspective is to provide conceptual, molecular modeling, and experimental support for the validity of these thermodynamic combined equilibrium equations down to the smallest interfacial radii of curvature. Important concepts underpinning thermodynamics, including ensemble averaging and Gibbs’s treatment of bulk phase heterogeneities in the region of an interface, give reason to believe that these equations might be valid to smaller scales than was previously thought. There is significant molecular modeling and experimental support for all three of the Kelvin equation, the Gibbs–Thomson equation, and the Ostwald–Freundlich equation for interfacial radii of curvature from 1 to 4 nm. There is even evidence of sub-nanometer quantitative accuracy for the Kelvin equation and the Gibbs–Thomson equation.
Cross-correlation corrected friction in (generalized) Langevin models
Authors: Klippenstein Viktor , van der Vegt Nico F. A.
Published: May 2021

We propose a route for parameterizing isotropic (generalized) Langevin [(G)LE] thermostats with the aim to correct the dynamics of coarse-grained (CG) models with pairwise conservative interactions. The approach is based on the Mori–Zwanzig formalism and derives the memory kernels from Q-projected time correlation functions. Bottom-up informed (GLE and LE) thermostats for a CG star-polymer melt are investigated, and it is demonstrated that the inclusion of memory in the CG simulation leads to predictions of polymer diffusion in quantitative agreement with fine-grained simulations. Interestingly, memory effects are observed in the diffusive regime. We demonstrate that previously neglected cross-correlations between the “irrelevant” and the CG degree of freedom are important and lie at the origin of shortcomings in previous CG simulations.
Effect of local structure and stoichiometry on the dynamic behavior of bi-metal interfaces
Authors: Chen J. , Fensin S. J.
Published: May 2021

Molecular dynamics (MD) simulations are performed to investigate the failure behavior of Al/Al, Al/Fe, and Al/AlFe bi-layers under high strain-rate shock loading. Additional simulations are performed to invesigate solely the tensile response of these systems and to isolate the effects of loading history on damage and failure. Specifically, the compression stage of the shock is excluded from the tensile simulations. This work shows that local structure variation, including the introduction of serrations, plays different roles in controlling damage nucleation depending on the specific loading condition. Under shock loading, the stress for void nucleation and the resulting void distribution is insensitive to an interface structure, whereas under pure tensile loading, the opposite is true, even though the strain rate is comparable. The above difference can be explained based on the corresponding change in the total deformation prior to damage nucleation under shock loading, which is missing from the pure tensile loading. Therefore, it is concluded that whether local interface structure matters under high strain-rate loading depends on the specific loading history and the stress state: the local structure variation matters only when it alters the deformation behavior, and subsequently, damage nucleation and evolution.
Hole formation effect on surface morphological response of plasma-facing tungsten
Authors: Chen Chao-Shou , Dasgupta Dwaipayan , Wirth Brian D. , Maroudas Dimitrios
Published: May 2021

We report simulation results on the effect of helium (He) bubble bursting-mediated surface hole formation on the surface morphological response of tungsten plasma-facing components (PFCs) in nuclear fusion devices. Our analysis is based on an atomistically informed, continuum-scale model, which is capable of accessing the spatiotemporal scales relevant to the fuzz nanostructure formation process on the surface of PFC tungsten. Our simulations account, in an empirical fashion, for two types of subsurface bubble dynamical phenomena in the nanobubble region of PFC tungsten during He plasma irradiation, involving bubble bursting and surface crater formation. We demonstrate that the hole formation effect on the PFC tungsten surface accelerates the growth rate of nanotendrils and the onset of fuzz formation. As a result, the predicted incubation time for surface nanotendril growth is shortened, in agreement with experimental data of incubation fluence at comparable plasma exposure conditions. We also explore systematically the dependence of the PFC surface morphological response on the areal density of holes introduced at regular time intervals onto the He-implanted tungsten surface, a parameter in our analysis that serves as a proxy for the rate of He bubble bursting. More importantly, our simulations capture fine surface features in the PFC tungsten surface morphology and predict that the average spacing between nanotendrils is on the order of 100  nm, consistent with the experimental findings.
Quadcopter drones swarm aeroacoustics
Authors: Dbouk Talib , Drikakis Dimitris
Published: May 2021

Swarms of drones is an emerging field of research and technology. Multicopter drones are noisy machines, and the noise effects would increase for a swarm. It is, therefore, essential to understand what flight formation conditions would reduce noise emissions. This study concerns the noise induced by drone swarms. We developed a high-resolution computational methodology for predicting aeroacoustic footprints emitted from a swarm of multi-copter drones. We show that a V-flight formation emits less sound pressure level noise than a U-shape (or rectangular) formation. We also demonstrate that the V-shape flight formation induces reduced drag, thus saving energy. This research's impact is broad, including defence and security, public health, transportation, and surveillance, among others.
Sorption methods in marine radiochemistry
Authors: Dovhyi Illarion I. , Bezhin Nikolay A. , Tananaev Ivan G.
Published: May 2021

The review presents the general methodology of using sorption methods to solve problems of marine radiochemistry, including sampling, preconcentration and radiochemical preparation and methods for measuring the activity of radionuclides. The possible methodological errors at various stages of sampling and sample concentration are discussed. The most widely used artificial (90Sr,134Cs,137Cs,239Pu,240Pu), natural (210Pb,210Po; radium quartet:223Ra,224Ra,226Ra,228Ra; thorium isotopes, mainly234Th) and cosmogenic (7Be,32P,33P) radiotracers are considered. The sorption of uranium from seawater is not addressed, since its concentration in seawater is usually calculated from the known dependence of uranium concentration on seawater salinity.

The bibliography includes 200 references.
Pharmacological inhibition of PI5P4Kα/β disrupts cell energy metabolism and selectively kills p53-null tumor cells
Authors: Chen Song , Chandra Tjin Caroline , Gao Xiang , Xue Yi , Jiao Haoyan , Zhang Ruilin , Wu Mengnan , He Zunyu , Ellman Jonathan , Ha Ya
Published: May 2021

Significance

Phosphatidylinositol 5-phosphate 4-kinases PI5P4Kα and PI5P4Kβ are essential for the development of late-onset tumors in mice with germline p53 deletion. The mechanism underlying their synthetic lethality was previously undefined. Here, we leverage structural insights of the lipid kinase to develop a highly potent and selective noncovalent inhibitor for PI5P4Kα/β. We show that pharmacological inhibition of PI5P4Kα/β disrupts cell energy homeostasis, causing AMPK activation and mTORC1 inhibition. Feedback through the S6K/insulin receptor substrate (IRS) loop contributes to insulin hypersensitivity and enhanced PI3K signaling. Most significantly, the energy stress induced by PI5P4Kα/β inhibition is selectively toxic toward p53-null tumor cells. The chemical probe may lead to a novel class of diabetes and cancer drugs.
G-quadruplex structural variations in human genome associated with single-nucleotide variations and their impact on gene activity
Authors: Gong Jia-yuan , Wen Cui-jiao , Tang Ming-liang , Duan Rui-fang , Chen Juan-nan , Zhang Jia-yu , Zheng Ke-wei , He Yi-de , Hao Yu-hua , Yu Qun , Ren Su-ping , Tan Zheng
Published: May 2021

Significance

Our work reveals the genome-wide prevalence of G4 structural variations (G4Vs) associated with single-nucleotide variations (SNVs) in the human genome and how such G4Vs interact with gene-regulatory elements and subsequently affect the activities of genes accommodating the G4Vs. The G4Vs are enriched in genes around transcription start sites, implying their potential involvement in gene expression. Because G4 structures participate in essential physiological and pathological processes, the G4Vs should make crucial contributions to the genotype and phenotype connection and serve as potential therapeutic targets for personalized remedies and medicine.
Moving beyond the constraints of chemistry via crystal structure discovery with isotropic multiwell pair potentials
Authors: Dshemuchadse Julia , Damasceno Pablo F. , Phillips Carolyn L. , Engel Michael , Glotzer Sharon C.
Published: May 2021

Significance

Which crystal structures are possible if the restrictions of the quantum realm are lifted? Our knowledge of ordered particle geometries was previously restricted to the kinds of structures observable in hard condensed matter—on the atomic scale. Here, we use freely tunable computational models to represent particles with variable properties, and we determine the crystal structures into which they self-assemble. The resulting arrangements often correspond to structures known from atomic-scale materials; however, we discover a comparable number of previously unknown crystal structures with different local coordination motifs, incompatible with the limitations of the chemical bond. Our results can be used to engineer soft condensed matter with unprecedented, ordered geometries, paving the way toward materials with potentially novel properties.
Thermal resistance effect on anomalous diffusion of molecules under confinement
Authors: Yuan Jiamin , Liu Zhiqiang , Wu Yimo , Han Jingfeng , Tang Xiaomin , Li Chengbin , Chen Wei , Yi Xianfeng , Zhou Jian , Krishna Rajamani , Sastre German , Zheng Anmin
Published: May 2021

Significance

Diffusion is the primary process in practical multidisciplinary areas such as separation and catalysis. Transportation is usually positively correlated with temperature due to thermal motion. We show here an anomalous phenomenon wherein a higher temperature effectively slows diffusion for linear-chain hydrocarbon molecules under confinement. Such an obstruction in diffusion results from the novel mechanism of “thermal resistance effect,” in which the configuration of a guest molecule is significantly deformed with temperature effect and then strongly restrains the process of transportation in nanoscale channels at high temperature. This work will enrich our understanding of an anomalous mechanism of the diffusion phenomenon and could shed light on a fundamental understanding of the diffusion process.
Much work remains to reach consensus on musculoskeletal injury risk in military service members: A systematic review with meta‐analysis
Authors: Rhon Daniel I. , Molloy Joseph M. , Monnier Andreas , Hando Ben R. , Newman Phillip M.
Published: May 2021

Musculoskeletal injuries are the most common reason military service members cannot perform their military duties. Not only are they costly and associated with long‐term disability, often long after completion of military service, but injuries also adversely affect the military readiness of a nation. This can be seen as a threat to national security and part of the impetus behind many efforts to better understand, predict, and mitigate injury risk in the military. A systematic review of the literature published between 1995 and October 31, 2020 was conducted to identify significant risk factors of musculoskeletal injury in military populations across the world. 74 out of 170 eligible studies addressed comprehensive injuries, providing 994 unique risk factors. 46 of these studies provided data that could be included in a meta‐analysis, which was possible for 15 predictor variables. Seven predictors were significant in meta‐analysis: female sex(RR=1.46;95CI 1.30,1.64), high body mass index(RR=1.36;95CI 1.21,1.53), functional movement screen pain (RR=1.70;95CI 1.55,1.87) or scores ≤ 14(RR=1.42 95CI 1.29,1.56), prior injury(RR=1.54;95CI 1.32,1.80), slower running performance(RR=1.33;95CI 1.18,1.51), and poorer push‐up performance(RR=1.15;95CI 1.04,1.27). Low BMI, height, weight, smoking, physical activity scores, and sit‐up and jump performance were not significant risk factors in the meta‐analysis. Most studies had a high risk of bias. Lack of raw data and large heterogeneity in definitions of predictors and injury outcomes limited comparison across many studies.

Highlights

Female sex, high body mass index, pain with functional movement screen or a score of ≤ 14, prior injury, slower running performance and poorer push‐up performance were all significant predictors of musculoskeletal injury.

Low body mass index, height, weight, smoking, physical activity scores, and sit‐up and jump performance were not significant predictors of musculoskeletal injury.

Many other predictors were present only in single studies, but large heterogeneity in definitions of both outcomes and predictors limited comparison across studies.

Overall, studies assessing risk factors to predict musculoskeletal injuries in the military were at high risk for bias, especially in regards to statistical approaches.
Poincare–Einstein approach to Penrose’s conformal cyclic cosmology
*
Authors: Nurowski Paweł
Published: May 2021

We consider two consecutive eons in Penrose’s conformal cyclic cosmology and study how the matter content of the past eon determines the matter content of the present eon by means of the reciprocity hypothesis of Roger Penrose. We assume that the only matter content in the final stages of the past eon is a spherical wave described by Einstein’s equations with a pure radiation energy momentum tensor and with a cosmological constant. Using the Poincare-Einstein type of expansion to determine the metric in the past eon, applying the reciprocity hypothesis to get the metric in the present eon, and using the Einstein equations in the present eon to interpret its matter content, we show that the single spherical wave from the previous eon in the new eon splits into three portions of radiation: the two spherical waves, one which is a damped continuation from the previous eon, the other is focusing in the new eon as it encountered a mirror at the Big Bang surface, and in addition a lump of scattered radiation described by the statistical physics.
The speed of sound in monster sound tubes
Authors: Klomp Joe , Schmit Nathaniel Ulmer , Sidebottom David L
Published: May 2021

We present a study of the slowing of sound by a corrugated drainage pipe that serves as a straightforward project lab investigation for undergraduate students.
A Bayesian approach to tissue-fraction estimation for oncological PET segmentation
Authors: Liu Ziping , Mhlanga Joyce C , Laforest Richard , Derenoncourt Paul-Robert , Siegel Barry A , Jha Abhinav K
Published: May 2021

Tumor segmentation in oncological PET is challenging, a major reason being the partial-volume effects (PVEs) that arise due to low system resolution and finite voxel size. The latter results in tissue-fraction effects (TFEs), i.e. voxels contain a mixture of tissue classes. Conventional segmentation methods are typically designed to assign each image voxel as belonging to a certain tissue class. Thus, these methods are inherently limited in modeling TFEs. To address the challenge of accounting for PVEs, and in particular, TFEs, we propose a Bayesian approach to tissue-fraction estimation for oncological PET segmentation. Specifically, this Bayesian approach estimates the posterior mean of the fractional volume that the tumor occupies within each image voxel. The proposed method, implemented using a deep-learning-based technique, was first evaluated using clinically realistic 2D simulation studies with known ground truth, in the context of segmenting the primary tumor in PET images of patients with lung cancer. The evaluation studies demonstrated that the method accurately estimated the tumor-fraction areas and significantly outperformed widely used conventional PET segmentation methods, including a U-net-based method, on the task of segmenting the tumor. In addition, the proposed method was relatively insensitive to PVEs and yielded reliable tumor segmentation for different clinical-scanner configurations. The method was then evaluated using clinical images of patients with stage IIB/III non-small cell lung cancer from ACRIN 6668/RTOG 0235 multi-center clinical trial. Here, the results showed that the proposed method significantly outperformed all other considered methods and yielded accurate tumor segmentation on patient images with Dice similarity coefficient (DSC) of 0.82 (95% CI: 0.78, 0.86). In particular, the method accurately segmented relatively small tumors, yielding a high DSC of 0.77 for the smallest segmented cross-section of 1.30 cm2. Overall, this study demonstrates the efficacy of the proposed method to accurately segment tumors in PET images.
Effective fermion mass in relativistic and non-relativistic systems
Authors: Caldas Heron
Published: May 2021

Electrons interact strongly with their environment. The result of these interactions is, most of the time, encoded in an effective mass. In non-relativistic systems, as in condensed matter, the electrons plus interactions form a quasiparticle with an effective mass. From the side of relativistic systems, the fermions also acquire an effective mass due to the interactions with the surrounding medium. We employ a non-perturbative method to calculate the effective mass of relativistic and non-relativistic fermions, in various situations. We find the effective masses up to second order of the iteration method. The results can be of interest in current studies on fermion systems.
Cosmological trans-Planckian conjectures are not effective
Authors: Burgess C.P. , de Alwis S.P. , Quevedo F.
Published: May 2021

It is remarkable that the primordial fluctuations as revealed by the CMB coincide with what quantum fluctuations would look like if they were stretched across the sky by accelerated cosmic expansion. It has been observed that this same stretching also brings very small — even trans-Planckian — length scales up to observable sizes if extrapolated far enough into the past. This potentially jeopardizes later descriptions of late-time cosmology by introducing uncontrolled trans-Planckian theoretical errors into all calculations. Recent speculations, such as the Trans-Planckian Censorship Conjecture (TCC), have been developed to avoid this problem. We revisit old arguments why the consistency of (and control over) the Effective Field Theory (EFT) governing late-time cosmology is not necessarily threatened by the descent of modes due to universal expansion, even if EFT methods may break down at much earlier times. Failure of EFT methods only poses a problem if late-time predictions rely on non-adiabatic behaviour at these early times (such as is often true for bouncing cosmologies, for example). We illustrate our arguments using simple non-gravitational examples such as slowly rolling scalar fields and the spacing between Landau levels for charged particles in slowly varying magnetic fields, for which similar issues arise and are easier to understand. We comment on issues associated with UV completions. Our arguments need not invalidate speculative ideas like the TCC but suggest they are not required by the present evidence.
Exploration of electron vortices in the photoionization of diatomic molecules in intense laser fields
Authors: Guo Jing , Zhang Si-Qi , Zhang Jun , Zhou Sheng-Peng , Guan Peng-Fei
Published: May 2021

Based on the approach within the single-electron approximation (SEA) frame, we numerically solve the two-dimensional (2D) time-dependent Schr

o

¨

dinger equation of N2 molecules under co-rotating and counter-rotating circularly polarized attosecond pulses. The vortex structure appears in counter-rotating circularly laser fields rather than the co-rotating case. The calculated vortex structures corresponding to the photoionization are found to be sensitive to the time delays T

d
of the two pulses, laser ellipticities and carrier envelope phases (CEPs). As the ellipticity increases to 1, the momentum distribution rotates and a vortex structure appears, and the interference is proved to play an important role in momentum distribution. The vortex structures also rotate clockwisely as the relative CEPs increase. The arms of the vortex structure become longer and thinner with the increasing T

d
. All these phenomena can be well understood by the attosecond perturbation ionization theory and the interference effect. Our findings clarify the applicability of the SEA model of diatomic molecules in attosecond extreme-ultraviolet fields.
Quantum computation and simulation with vibrational modes of trapped ions
Authors: Chen Wentao , Gan Jaren , Zhang Jing-Ning , Matuskevich Dzmitry , Kim Kihwan
Published: May 2021

Vibrational degrees of freedom in trapped-ion systems have recently been gaining attention as a quantum resource, beyond the role as a mediator for entangling quantum operations on internal degrees of freedom, because of the large available Hilbert space. The vibrational modes can be represented as quantum harmonic oscillators and thus offer a Hilbert space with infinite dimensions. Here we review recent theoretical and experimental progress in the coherent manipulation of the vibrational modes, including bosonic encoding schemes in quantum information, reliable and efficient measurement techniques, and quantum operations that allow various quantum simulations and quantum computation algorithms. We describe experiments using the vibrational modes, including the preparation of non-classical states, molecular vibronic sampling, and applications in quantum thermodynamics. We finally discuss the potential prospects and challenges of trapped-ion vibrational-mode quantum information processing.
Surface-enhanced Raman spectroscopy chips based on two-dimensional materials beyond graphene
Authors: Zhang Enqing , Xing Zhengkun , Wan Dian , Gao Haoran , Han Yingdong , Gao Yisheng , Hu Haofeng , Cheng Zhenzhou , Liu Tiegen
Published: May 2021

Surface-enhanced Raman spectroscopy (SERS) based on two-dimensional (2D) materials has attracted great attention over the past decade. Compared with metallic materials, which enhance Raman signals via the surface plasmon effect, 2D materials integrated on silicon substrates are ideal for use in the fabrication of plasmon-free SERS chips, with the advantages of outstanding fluorescence quenching capability, excellent biomolecular compatibility, tunable Fermi levels, and potentially low-cost material preparation. Moreover, recent studies have shown that the limits of detection of 2D-material-based SERS may be comparable with those of metallic substrates, which has aroused significant research interest. In this review, we comprehensively summarize the advances in SERS chips based on 2D materials. As several excellent reviews of graphene-enhanced Raman spectroscopy have been published in the past decade, here, we focus only on 2D materials beyond graphene, i.e., transition metal dichalcogenides, black phosphorus, hexagonal boron nitride, 2D titanium carbide or nitride, and their heterostructures. We hope that this paper can serve as a useful reference for researchers specializing in 2D materials, spectroscopy, and diverse applications related to chemical and biological sensing.
Compact SPAD pixels with fast and accurate photon counting in the analog domain
Authors: Ma Zhiqiang , Wu Zhong , Xu Yue
Published: May 2021

A compact pixel for single-photon detection in the analog domain is presented. The pixel integrates a single-photon avalanche diode (SPAD), a passive quenching & active recharging circuit (PQARC), and an analog counter for fast and accurate sensing and counting of photons. Fabricated in a standard 0.18 µm CMOS technology, the simulated and experimental results reveal that the dead time of the PQARC is about 8 ns and the maximum photon-counting rate can reach 125 Mcps (counting per second). The analog counter can achieve an 8-bit counting range with a voltage step of 6.9 mV. The differential nonlinearity (DNL) and integral nonlinearity (INL) of the analog counter are within the ± 0.6 and ± 1.2 LSB, respectively, indicating high linearity of photon counting. Due to its simple circuit structure and compact layout configuration, the total area occupation of the presented pixel is about 1500 μm2, leading to a high fill factor of 9.2%. The presented in-pixel front-end circuit is very suitable for the high-density array integration of SPAD sensors.
Yet another artefact rejection study: an exploration of cleaning methods for biological and neuromodulatory noise
Authors: Barban Federico , Chiappalone Michela , Bonassi Gaia , Mantini Dante , Semprini Marianna
Published: May 2021

Objective. Electroencephalography (EEG) cleaning has been a longstanding issue in the research community. In recent times, huge leaps have been made in the field, resulting in very promising techniques to address the issue. The most widespread ones rely on a family of mathematical methods known as blind source separation (BSS), ideally capable of separating artefactual signals from the brain originated ones. However, corruption of EEG data still remains a problem, especially in real life scenario where a mixture of artefact components affects the signal and thus correctly choosing the correct cleaning procedure can be non trivial. Our aim is here to evaluate and score the plethora of available BSS-based cleaning methods, providing an overview of their advantages and downsides and of their best field of application. Approach. To address this, we here first characterized and modeled different types of artefact, i.e. arising from muscular or blinking activity as well as from transcranial alternate current stimulation. We then tested and scored several BSS-based cleaning procedures on semi-synthetic datasets corrupted by the previously modeled noise sources. Finally, we built a lifelike dataset affected by many artefactual components. We tested an iterative multistep approach combining different BSS steps, aimed at sequentially removing each specific artefactual component. Main results. We did not find an overall best method, as different scenarios require different approaches. We therefore provided an overview of the performance in terms of both reconstruction accuracy and computational burden of each method in different use cases. Significance. Our work provides insightful guidelines for signal cleaning procedures in the EEG related field.
α-boson gas model based on α-additive entropy
Authors: Chung Won Sang , Hassanabadi Hassan , Lütfüoğlu Bekir Can
Published: May 2021

In this paper, we consider the grand partition function for an α-boson gas. First, we revisit the thermodynamic laws and functions in this formalism. Then, we explore α-boson gas condensation and show that the critical temperature at which α-boson condensation begins depends on the shape of the container. In particular, we compute the critical temperature for a cubic container. Finally, we discuss the α-deformed virial expansion for α-boson gas.
The Adoption of ICT in Libyan Higher Education Institutions (LHEIs): Theoretical Models and Challenges
Authors: Mhamed Alshref Halema H. , Abas Hafiza , Abu Bakar Nur Azaliah
Published: May 2021

The adoption of eLearning in developing countries is rare when a comparison is made against the developed nations. Therefore, this study answered calls from numerous literature demanding for more research to investigate the adoption, usage, and application of eLearning systems and applications in Libyan higher education institutions (LHEIs) to contribute to this crucial knowledge gap. Thus, a systematic literature review (SLR) was conducted focusing on the eLearning technology acceptance theories and models and open issues and challenges facing the LHEIs. Hence, the findings revealed that the technology acceptance model (TAM) is the most dominant theoretical model applied to test the adoption of eLearning in LHEIs. The finding further revealed that there are limited studies based on other technology acceptance theories such as the unified theory of acceptance and use of technology (UTAUT), the theory of reasoned action (TRA), and the theory of planned behavior (TPB). Hence, this study recommends the adoption of the UTAUT framework for future research due to its foundation from eight different technology acceptance models, including the dominant TAM theory, which could offer new insights. The findings of this study have the potential for academic researchers wanting to study the acceptance and use of technology for teaching and learning especially in developing countries.
Improving K-means clustering based on firefly algorithm
Authors: Al Radhwani Amal Mahmood Naji , Algamal Zakariya Yahya
Published: May 2021

Data clustering determines a group of patterns in a dataset which are homogeneous in nature. The objective is to develop an automatic algorithm which can accurately classify an unleveled dataset into groups. The K-means method is the most fundamental partitioned clustering concept. However, the performance of K-means method is fully depending on determining the number of clusters, K, and determining the optimal centroid for performing the clustering process. In this paper, an adaptive firefly optimization algorithm, which is a nature-inspired algorithm, is employed to improve the K-means clustering. The experimental results of clustering two real datasets show that the proposed method is able to effectively outperform other alternatives methods.
Shrinkage estimators for semiparametric regression model
Authors: Mohammed Hadi Salman , Algamal Zakariya Yahya
Published: May 2021

Semiparametric regression models are extensions of linear regression models to include a nonparametric function of some explanatory variables. In semiparametric regression model researchers often encounter the problem of multicollinearity. In the context of ridge estimator, the estimation of shrinkage parameter plays an important role in analyzing data. In this paper, numerous selection methods of the shrinkage parameter of ridge estimator are explored and investigated. Our Monte Carlo simulation results suggest that some estimators can bring significant improvement relative to others, in terms of mean squared error.
A New Left Truncated Gumbel Distribution: Properties and Estimation
Authors: Neamah M W , Qasim B A
Published: May 2021

Gumbel probability distribution is an important probability distribution that has wide applications in various fields such as engineering, physics, hydrology, geology, etc. The study aims to generate a new truncated distribution by truncate the probability density function of the first type Gumbel distribution from the left side to obtain the Truncated Gumbel distribution from the left side within the period (0, ∞). As we work in this paper on the derivation of the new truncated distribution formula and its characteristics. As well as discussing different methods of estimating its parameters, represented by the maximum likelihood method and Percentiles Estimation Method, then making a simulation of the comparison between methods of estimation.
Quantitative Structure-Activity Relationship Modeling Based on Improving Penalized Linear Regression Model
Authors: Shamany Rehad Emad , Algamal Zakariya Yahya
Published: May 2021

One of the powerful and a promising model which is used to understand the structural relationship between the chemical activity and the chemical compounds is the quantitative structure-activity relationship (QSAR). However, the huge in dimensionality is one of the major problems which affect the quality of the QSAR modeling. Penalized methods are an attractive framework that have been adapted and gained popularity among researchers as the key for performing descriptor selection and QSAR model estimation simultaneously. The choice of the tuning parameter of the penalized methods is critical. Our aim of this paper is to efficiently estimate such a tuning parameter by using bat algorithm (BA), which is a king of nature-inspired algorithms. Experimental results, obtained by running on two datasets, show that our proposed method performs better than other methods, in terms of prediction, number of selected descriptors, and running time. Further, the Y-randomization test and applicability domain confirm that the constructed QSAR model by BA method is reliable and robust.
Regularized MAVE through the elastic net with correlated predictors
Authors: Alkenani A , Rahman E
Published: May 2021

In this article, we proposed a model-free variable selection method (SMAVE-EN). The concepts of sufficient dimension reduction (SDR) and regularization methods are combined to introduce SMAVE-EN. This method is proposed to produce a shrinkage estimation when the predictors are highly correlated under SDR settings. The advantage of SMAVE-EN is that SMAVE-EN extended Elastic net (EN) to nonlinear and multi-dimensional regression under SDR settings. From another side, the SMAVE-EN enables MAVE to work with problems were the predictors are highly correlated. In addition, SMAVE-EN can exhaustively estimate dimensions, while selecting informative covariates simultaneously under SDR framework. The effectiveness of SMAVE-EN is evaluated by both simulation and real data analysis.