Unbiased Case Research Articles

The mean exiting time for the biased correlated random walk characterized by a system of first-order PDEs

A biased correlated random walk (BCRW) is a stochastic process that models individual movement and other similar practical phenomena. This paper studies the mean exiting time of a BCRW in a finite interval, subject to a system of first-order PDEs. The interval has two scenarios: (i) both ends are absorbing; and (ii) one end is absorbing and the other end is reflecting. We obtain an exact formula for the mean exiting time of a particle as a function of its speed, turning rates, and initial position. Using the mean exiting time, we also derive the mean first passage time for a particle to reach the boundary. Our approach enables us to infer relevant parameters from experimental data, or to manipulate the mean exiting time and the first passage time by choosing the initial position of the particle suitably. The unbiased case is a special case of the biased case when the right-turning rate equals the left-turning rate.

Abstract PO5-18-05: Assessment of the Potential of Photon mini-GRID Therapy for Pre-operative Partial Breast Cancer Treatment

Abstract Purpose We propose a new spatially fractionated radiation therapy (SFRT) technique, called mini-GRID therapy, to reduce normal tissue toxicities in pre-operative partial breast cancer radiotherapy. Mini-GRID therapy, an optimized implementation of GRID therapy, utilizes very narrow beams (widths ~ 1-2 mm) which significantly increase normal tissue tolerances. The concept, proposed by our team in 2017 [1], has been successfully implemented at Hospital de Santiago de Compostela (Spain) showing excellent results in terms of brain toxicity reduction [2]. Profiting from this remarkable increase in tolerance, this study aims to evaluate the feasibility and efficacy of photon mini-GRID therapy for pre-operative partial breast cancer treatment. Methods Ten unbiased clinical cases were selected for the study, comparing photon mini-GRID therapy with conventional broad beam radiotherapy. Monte Carlo simulations (TOPAS v.3.6) were performed based on the mini-GRID therapy implementation (megavoltage X-rays, Varian flattening-filter-free LINAC) realized at the University Hospital in Santiago de Compostela. A mean dose of 24 Gy was delivered in the PTV using three photon mini-GRID arrays with mini beams of approximately 1.8x1.8 mm² at the isocenter. The study aimed to achieve better tumor coverage than conventional pre-operative radiotherapy while ensuring comparable skin toxicity. Valley doses, determining tissue-sparing effects, were compared against organs-at-risk (OARs) tolerance limits. Results The mini-GRID therapy treatments ensured partial tumor coverage and met the dose tolerance limits for all the considered OARs, the most challenging of all being the skin [3]. Peak-to-valley dose ratio (PVDR) in the skin was higher than 3.5 for all the considered patients. Compared to standard radiotherapy (SRT) plans, mini-GRID therapy significantly reduced mean doses to the lungs, heart, and chest wall in the studied cases. Conclusion In this proof-of-concept study, we evaluated photon mini-GRID therapy with megavoltage X-rays as an alternative treatment approach for pre-operative partial breast cancer irradiation, demonstrating its feasibility and straightforward implementation. Because of its high skin and normal tissue-sparing capacities, photon mini-GRID therapy has great potential to improve pre-operative treatment outcomes. Complementary studies and clinical validation are needed to fully establish the optimal protocols and assess long-term effects, but the results encourage the integration of photon mini-GRID therapy as a promising modality for breast cancer therapy.

Investigating the technical quality of undergraduate endodontic treatment in a primary care-based dental school.

Introduction The success of root canal treatment (RCTx) relies on the technical quality of the root canal filling, often assessed through radiographic evaluation.Aims This audit aims to evaluate the technical proficiency of Peninsula Dental School (PDS) undergraduate dental students in RCTx, comparing it with established European standards.Design Conducted as a retrospective study, this evaluation focuses on assessing the technical quality of RCTx performed by undergraduate dental students at PDS across various academic years.Setting PDS, a primary care-based dental school in the UK, serves as the focal point for this evaluation.Materials and methods Reviewed 2021-2022 endodontic cases by supervised undergraduates. Analysed radiographs for obturation, voids and errors based on established benchmarks. Randomly selected unbiased cases, assessing voids, filling proximity, missed canals and canal anatomy preservation.Interventions Comparative analysis of RCTx quality between PDS students and counterparts from other dental schools, exemplified by Dublin Dental University Hospital (DDUH).Results Findings revealed that 62.07% of single-rooted and 60% of multi-rooted teeth treated by PDS students met European standards.Discussion The implications highlight the proficiency of PDS students in RCTx, comparing favourably to DDUH.Conclusion Recommendations emphasise conducting regular educational audits in dental schools to continually enhance RCTx techniques and ensure high-quality clinical teaching.

Theory on Electron–Phonon Spin Dephasing in GaAs Multi‐Electron Double Quantum Dots

AbstractRecent studies reveal that a double‐quantum‐dot system hosting more than two electrons may be superior in certain aspects as compared to the traditional case in which only two electrons are confined (a singlet–triplet qubit). The electron–phonon dephasing occurring in a GaAs multi‐electron double‐quantum‐dot system is studied, in a biased case in which the singlet state is hybridized, as well as in an unbiased case in which the hybridization is absent. It is found that while the electron–phonon dephasing rate increases with the number of electrons confined in the unbiased case, this does not hold in the biased case. A merit figure is defined as a ratio between the exchange energy and the dephasing rate, and have shown that in experimentally relevant range of the exchange energy, the merit figure actually increases with the number of electrons in the biased case. The results show that the multi‐electron quantum‐dot system has another advantage in mitigating the effect of electron–phonon dephasing, which is previously under‐appreciated in the literature.

Electron trapping in magnetic driven graphene quantum dots

In this paper we present an in-depth theoretical investigation of an electron scattering process on a graphene quantum dot (GQD) supposed to a perpendicular magnetic field. As it is well known, because of Klein tunneling, an electrostatic potential is not helpful to localize an electron inside a GQD. However, we report here that in the case of a magnetic driven GQD, there emerge scattering resonances characterized by trapped electronic states inside the dot for finite periods of time, otherwise known as quasi-bound states. Using a real space scattering analysis, we highlight in a very intuitive manner how the quasi-bound states are generated and, for a comprehensive investigation, we evaluate their corresponding lifetime (trapping time). As well, we explore the case of an electrostatically biased GQD. We show that this configuration may be very advantageous regarding the control of the trapping times which reach values much higher than in the unbiased case.

The microwave properties of tin sulfide thin films prepared by RF magnetron sputtering techniques

In this paper we present the microwave properties of tin sulfide (SnS) thin films with the thickness of just 10 nm, grown by RF magnetron sputtering techniques on a 4 inch silicon dioxide/high-resistivity silicon wafer. In this respect, interdigitated capacitors in coplanar waveguide technology were fabricated directly on the SnS film to be used as both phase shifters and detectors, depending on the ferroelectric or semiconductor behaviour of the SnS material. The ferroelectricity of the semiconducting thin layer manifests itself in a strong dependence of the electrical permittivity on the applied DC bias voltage, which induces a phase shift of 30 degrees mm−1 at 1 GHz and of 8 degrees mm−1 at 10 GHz, whereas the transmission losses are less than 2 dB in the frequency range 2–20 GHz. We have also investigated the microwave detection properties of SnS, obtaining at 1 GHz a voltage responsivity of about 30 mV mW−1 in the unbiased case and with an input power level of only 16 μW.

OMARU: a robust and multifaceted pipeline for metagenome-wide association study.

Microbiome is an essential omics layer to elucidate disease pathophysiology. However, we face a challenge of low reproducibility in microbiome studies, partly due to a lack of standard analytical pipelines. Here, we developed OMARU (Omnibus metagenome-wide association study with robustness), a new end-to-end analysis workflow that covers a wide range of microbiome analysis from phylogenetic and functional profiling to case–control metagenome-wide association studies (MWAS). OMARU rigorously controls the statistical significance of the analysis results, including correction of hidden confounding factors and application of multiple testing comparisons. Furthermore, OMARU can evaluate pathway-level links between the metagenome and the germline genome-wide association study (i.e. MWAS-GWAS pathway interaction), as well as links between taxa and genes in the metagenome. OMARU is publicly available (https://github.com/toshi-kishikawa/OMARU), with a flexible workflow that can be customized by users. We applied OMARU to publicly available type 2 diabetes (T2D) and schizophrenia (SCZ) metagenomic data (n = 171 and 344, respectively), identifying disease biomarkers through comprehensive, multilateral, and unbiased case–control comparisons of metagenome (e.g. increased Streptococcus vestibularis in SCZ and disrupted diversity in T2D). OMARU improves accessibility and reproducibility in the microbiome research community. Robust and multifaceted results of OMARU reflect the dynamics of the microbiome authentically relevant to disease pathophysiology.

Plasmon modes in double-layer biased bilayer graphene

We investigate zero-temperature plasmon modes in a double-layer bilayer graphene structure under a perpendicular electrostatic bias. The numerical results demonstrate that there exist two collective modes which are undamped in the long wavelength limit. The finite potential bias decreases remarkably the plasmon energy in a wide range of wave-vector and makes plasmon branches become Landau damped at a higher wave-vector as compared to unbiased case. We find that the dependence of plasmon dispersions on the system parameters such as the inter-layer separation and carrier density is similar in two cases with and without electrostatic bias.

Controlling electrical and thermoelectric properties of bilayer SiC by bias voltage

The thermoelectric properties of bilayer SiC in the presence of bias voltage are investigated by using the tight binding model. The Green function and the Kubo-Greenwood formula are employed to investigate the temperature dependence of electric and thermal conductivities, heat capacity and paramagnetic susceptibility of biased bilayer SiC. Based on the first-principles calculation of bilayer SiC, we fit the sixth nearest neighbors intralayer and the fourth nearest neighbors interlayer tight-binding model parameters. Bilayer SiC is semiconductor with indirect band gap at K point. The band gap of bilayer SiC decreases linearly with increasing the bias voltage until reaches zero at critical voltage Uc = 2.08 eV, thereafter reopens and increases linearly by further increasing the bias voltage beyond Uc. The thermal functions increase with temperature to maximum then decrease with further temperature increasing. The increase occurs when the thermal energy is sufficient to excite charge carries from the valence bands to the conduction bands. The thermal properties are dependent to the bias voltage and in the low temperature range the biased bilayer SiC has higher thermal properties than that unbiased case, due to the band gap reduction. The thermoelectric figure of merit can be controlled by applying the bias voltage which leads to increasing the high temperature applications of the bilayer SiC.

A new link prediction in multiplex networks using topologically biased random walks

Link prediction is a technique to forecast future new or missing relationships between nodes based on the current network information. However, the link prediction in monoplex networks seems to have a long background, the attempts to accomplish the same task on multiplex networks are not abundant, and it was often a challenge to apply conventional similarity methods to multiplex networks. The issue of link prediction in multiplex networks is the way of predicting the links in one layer, taking structural information of other layers into account. One of the most important methods of link prediction in a monoplex network is a local random walk (LRW) that captures the network structure using pure random walking to measure nodes similarity of the graph and find unknown connections. The goal of this paper is to propose an extended version of local random walk based on pure random walking for solving link prediction in the multiplex network, referred to as the Multiplex Local Random Walk (MLRW). We explore approaches for leveraging information mined from inter-layer and intra-layer in a multiplex network to define a biased random walk for finding the probability of the appearance of a new link in one target layer. Experimental studies on seven multiplex networks in the real world demonstrate that a multiplex biased local random walk performs better than the state-of-the-art methods of link prediction and corresponding unbiased case and improves prediction accuracy.

The Multidisciplinary Management of Hepatocellular Carcinoma.

The Multidisciplinary Management of Hepatocellular Carcinoma.

Evaluating Rank-Coherence of Crowd Rating in Customer Satisfaction

Crowd rating is a continuous and public process of data gathering that allows the display of general quantitative opinions on a topic from online anonymous networks as they are crowds. Online platforms leveraged these technologies to improve predictive tasks in marketing. However, we argue for a different employment of crowd rating as a tool of public utility to support social contexts suffering to adverse selection, like tourism. This aim needs to deal with issues in both method of measurement and analysis of data, and with common biases associated to public disclosure of rating information. We propose an evaluative method to investigate fairness of common measures of rating procedures with the peculiar perspective of assessing linearity of the ranked outcomes. This is tested on a longitudinal observational case of 7 years of customer satisfaction ratings, for a total amount of 26.888 reviews. According to the results obtained from the sampled dataset, analysed with the proposed evaluative method, there is a trade-off between loss of (potentially) biased information on ratings and fairness of the resulting rankings. However, computing an ad hoc unbiased ranking case, the ranking outcome through the time-weighted measure is not significantly different from the ad hoc unbiased case.

A Caching Strategy Towards Maximal D2D Assisted Offloading Gain

Device-to-Device (D2D) communications incorporated with content caching have been regarded as a promising way to offload the cellular traffic data. In this paper, the caching strategy is investigated to maximize the D2D offloading gain with the comprehensive consideration of user collaborative characteristics as well as the physical transmission conditions. Specifically, for a given content, the number of interested users in different groups is different, and users always ask the most trustworthy user in proximity for D2D transmissions. An analytical expression of the D2D success probability is first derived, which represents the probability that the received signal to interference ratio is no less than a given threshold. As the formulated problem is non-convex, the optimal caching strategy for the special unbiased case is derived in a closed form, and a numerical searching algorithm is proposed to obtain the globally optimal solution for the general case. To reduce the computational complexity, an iterative algorithm based on the asymptotic approximation of the D2D success probability is proposed to obtain the solution that satisfies the Karush-Kuhn-Tucker conditions. The simulation results verify the effectiveness of the analytical results and show that the proposed algorithm outperforms the existing schemes in terms of offloading gain.

Biased Random Walk Conditioned on Survival Among Bernoulli Obstacles: Subcritical Phase

We consider a discrete time biased random walk conditioned to avoid Bernoulli obstacles on ${\mathbb Z}^d$ ($d\geq 2$) up to time $N$. This model is known to undergo a phase transition: for a large bias, the walk is ballistic whereas for a small bias, it is sub-ballistic. We prove that in the sub-ballistic phase, the random walk is contained in a ball of radius $O(N^{1/(d+2)})$, which is the same scale as for the unbiased case. As an intermediate step, we also prove large deviation principles for the endpoint distribution for the unbiased random walk at scales between $N^{1/(d+2)}$ and $o(N^{d/(d+2)})$. These results improve and complement earlier work by Sznitman [Ann. Sci. Ecole Norm. Sup. (4), 28(3):345--370, 371--390, 1995].

Tests of acoustic scale shifts in halo-based mock galaxy catalogues

ABSTRACT We utilize mock catalogues from high-accuracy cosmological N-body simulations to quantify shifts in the recovery of the acoustic scale that could potentially result from galaxy clustering bias. The relationship between galaxies and dark matter haloes presents a complicated source of systematic errors in modern redshift surveys, particularly when aiming to make cosmological measurements to sub-per cent precision. Apart from a scalar, linear bias parameter accounting for the density contrast ratio between matter tracers and the true matter distribution, other types of galaxy bias, such as assembly and velocity biases, may also significantly alter clustering signals from small to large scales. We create mocks based on generalized halo occupation populations of 36 periodic boxes from the abacus cosmosrelease, and test various biased models along with an unbiased base case in a total volume of $48 \, h^{-3} \, {\rm Gpc}^{3}$. Two reconstruction methods are applied to galaxy samples and the apparent acoustic scale is derived by fitting the two-point correlation function multipoles. With respect to the baseline, we find a 0.3 per cent shift in the line-of-sight acoustic scale for one variation in the satellite galaxy population, and we find a 0.7 per cent shift for an extreme level of velocity bias of the central galaxies. All other bias models are consistent with zero shift at the 0.2 per cent level after reconstruction. We note that the bias models explored are relatively large variations, producing sizeable and likely distinguishable changes in small-scale clustering, the modelling of which would further calibrate the baryon acoustic oscillations standard ruler.

Radiation Response of Negative Gate Biased SiC MOSFETs.

Silicon carbide (SiC) metal-oxide-semiconductor field effect transistors (MOSFETs) are expected as power electronic devices for high radiative conditions, including nuclear plants and space. Radiation response of commercial-grade prototype SiC MOSFETs with applying the gate bias is of interest, in terms of installation of the device in robots or sensors working under such radioactive circumstances. Due to gamma-rays irradiation, the threshold voltages (Vth) of samples with un- and negative-biased up to −4.5 V slightly shift toward the negative voltage side. In contrast, the positive bias of 2.25 V shifts Vth more negatively. Positive charge densities trapped in the gate oxide of un- and positive-biased samples increased with increasing dose. However, no significant increase was observed for negative-biased samples of −2.25 and −4.5 V. We calculated characteristic parameters for the accumulation of holes in the gate oxide, σpJp which is defined as the product of current density due to holes generated by irradiation and capture cross section for a hole in a trap, and it is lower for these negative biased samples compared with the unbiased case. Application of appropriate negative gate biases to SiC MOSFETs during irradiation suppresses accumulation of positive charges in the gate oxide and negative shift of Vth, due to irradiation.

Einstein relation and linear response in one-dimensional Mott variable-range hopping

We consider one-dimensional Mott variable-range hopping with a bias, and prove the linear response as well as the Einstein relation, under an assumption on the exponential moments of the distances between neighboring points. In a previous paper \cite{FGS} we gave conditions on ballisticity, and proved that in the ballistic case the environment viewed from the particle approaches, for almost any initial environment, a given steady state which is absolutely continuous with respect to the original law of the environment. Here, we show that this bias--dependent steady state has a derivative at zero in terms of the bias (linear response), and use this result to get the Einstein relation. Our approach is new: instead of using e.g. perturbation theory or regeneration times, we show that the Radon-Nikodym derivative of the bias--dependent steady state with respect to the equilibrium state in the unbiased case satisfies an $L^p$-bound, $p>2$, uniformly for small bias. This $L^p$-bound yields, by a general argument not involving our specific model, the statement about the linear response.

Effect of bias in a reaction-diffusion system in two dimensions.

We consider a single species reaction diffusion system on a two-dimensional lattice where the particles A are biased to move towards their nearest neighbors and annihilate as they meet. Allowing the bias to take both negative and positive values parametrically, any nonzero bias is seen to drastically affect the behavior of the system compared to the unbiased (simple diffusive) case. For positive bias, a finite number of dimers, which are isolated pairs of particles occurring as nearest neighbors, exist while for negative bias, a finite density of particles survives. Both the quantities vanish in a power-law manner close to the diffusive limit with different exponents. The appearance of dimers is exclusively due to the parallel updating scheme used in the simulation. The results indicate the presence of a continuous phase transition at the diffusive point. In addition, a discontinuity is observed at the fully positive bias limit. The persistence behavior is also analysed for the system.

Local Dimensions of Overlapping Self-Similar Measures

We show that any equicontractive, self-similar measure arising from the IFS of contractions \((S_{j})\), with self-similar set \([0,1]\), admits an isolated point in its set of local dimensions provided the images of \(S_{j}(0,1)\) (suitably) overlap and the minimal probability is associated with one (resp., both) of the endpoint contractions. Examples include \(m\)-fold convolution products of Bernoulli convolutions or Cantor measures with contraction factor exceeding \(1/(m+1)\) in the biased case and \(1/m\) in the unbiased case. We also obtain upper and lower bounds on the set of local dimensions for various Bernoulli convolutions.

Dissipative quantum mechanics beyond the Bloch-Redfield approximation: A consistent weak-coupling expansion of the Ohmic spin boson model at arbitrary bias

We study the time dynamics of the ohmic spin boson model at arbitrary bias $\epsilon$ and small coupling $\alpha$ to the bosonic bath. Using perturbation theory and the real-time renormalization group (RG) method we present a consistent zero-temperature weak-coupling expansion for the time evolution of the reduced density matrix one order beyond the Bloch-Redfield solution. We develop a renormalized perturbation theory and present an analytical solution covering the whole range from small to large times, including further results for exponentially small or large times. Resumming all secular terms in all orders of perturbation theory we find exponential decay for all terms of the time evolution. We determine the preexponential functions and find slowly varying logarithmic terms with the renormalized Rabi frequency $\Omega$ as energy scale together with strongly varying parts falling off asymptocially as $1/t$ in leading order, in contrast to the unbiased case. Resumming all logarithmic terms in all orders of perturbation theory via real-time RG we find the correct renormalized tunneling and a power-law behaviour for the oscillating modes with exponent crossing over from $2\alpha$ for exponentially small times to a bias-dependent value $2\alpha \epsilon^2/\Omega^2$ for exponentially large times. Furthermore, we present a degenerate perturbation theory to calculate consistently the purely decaying mode one order beyond Bloch-Redfield.