SearcharxivSearch

arXiv subjects

H. Yu

Publications and source records attributed to H. Yu.

At least 37 records · Page 2Linked to original sources

Multi-Modal Learning Using Physicians Diagnostics for Optical Coherence Tomography Classification

In this paper, we propose a framework that incorporates experts diagnostics and insights into the analysis of Optical Coherence Tomography (OCT) using multi-modal learning. To demonstrate the effectiveness of this approach, we create a medical diagnostic attribute dataset to improve disease classification using OCT. Although there have been successful attempts to deploy machine learning for disease classification in OCT, such methodologies lack the experts insights. We argue that injecting ophthalmological assessments as another supervision in a learning framework is of great importance for the machine learning process to perform accurate and interpretable classification. We demonstrate the proposed framework through comprehensive experiments that compare the effectiveness of combining diagnostic attribute features with latent visual representations and show that they surpass the state-of-the-art approach. Finally, we analyze the proposed dual-stream architecture and provide an insight that determine the components that contribute most to classification performance.

eess.IV

RIS-aided Zero-Forcing and Regularized Zero-Forcing Beamforming in Integrated Information and Energy Delivery

This paper considers a network of a multi-antenna array base station (BS) and a reconfigurable intelligent surface (RIS) to deliver both information to information users (IUs) and power to energy users (EUs). The RIS links the connection between the IUs and the BS as there is no direct path between the former and the latter. The EUs are located nearby the BS in order to effectively harvest energy from the high-power signal from the BS, while the much weaker signal reflected from the RIS hardly contributes to the EUs' harvested energy. To provide reliable links for all users over the same time-slot, we adopt the transmit time-switching (transmit-TS) approach, under which information and energy are delivered over different time-slot fractions. This allows us to rely on conjugate beamforming for energy links and zero-forcing/regularized zero-forcing beamforming (ZFB/RZFB) and on the programmable reflecting coefficients (PRCs) of the RIS for information links. We show that ZFB/RZFB and PRCs can be still separately optimized in their joint design, where PRC optimization is based on iterative closed-form expressions. We then develop a path-following algorithm for solving our max-min IU throughput optimization problem subject to a realistic constraint on the quality-of-energy-service in terms of the EUs' harvested energy thresholds. We also propose a new RZFB for substantially improving the IUs' throughput.

cs.IT

Deterministic Service Function Chaining over Beyond 5G Edge Fabric

Along with the increasing demand for latencysensitive services and applications, Deterministic Network (DetNet) concept has been recently proposed to investigate deterministic latency assurance for services featured with bounded latency requirements in 5G edge networks. The Network Function Virtualization (NFV) technology enables Internet Service Providers (ISPs) to flexibly place Virtual Network Functions (VNFs) achieving performance and cost benefits. Then, Service Function Chains (SFC) are formed by steering traffic through a series of VNF instances in a predefined order. Moreover, the required network resources and placement of VNF instances along SFC should be optimized to meet the deterministic latency requirements. Therefore, it is significant for ISPs to determine an optimal SFC deployment strategy to ensure network performance while improving the network revenue. In this paper, we jointly investigate the resource allocation and SFC placement in 5G edge networks for deterministic latency assurance. We formulate this problem as a mathematic programming model with the objective of maximizing the overall network profit for ISP. Furthermore, a novel Deterministic SFC deployment (Det-SFCD) algorithm is proposed to efficiently embed SFC requests with deterministic latency assurance. The performance evaluation results show that the proposed algorithm can provide better performance in terms of SFC request acceptance rate, network cost reduction, and network resource efficiency compared with benchmark strategy.

cs.NI

Opportunistic Relay in Multicast Channels with Generalized Shadowed Fading Effects: A Physical Layer Security Perspective

Through ordinary transmissions over wireless multicast networks are greatly hampered due to the simultaneous presence of fading and shadowing of wireless channels, secure transmissions can be enhanced by properly exploiting random attributes of the propagation medium. This study focuses on the utilization of those attributes to enhance the physical layer security (PLS) performance of a dual-hop wireless multicast network over kappa-mu shadow-fading channel under the wiretapping attempts of multiple eavesdroppers. In order to improve the secrecy level, the best relay selection strategy among multiple relays is employed. Performance analysis is carried out based on the mathematical modeling in terms of analytical expressions of non-zero secrecy capacity probability, secure outage probability, and ergodic secrecy capacity over multicast relay networks. Capitalizing on those expressions, the effects of system parameters, i.e., fading, shadowing, the number of antennas, destination receivers, eavesdroppers, and relays, on the secrecy performance are investigated. Numerical results show that the detrimental impacts caused by fading and shadowing can be remarkably mitigated using the well-known opportunistic relaying technique. Moreover, the proposed model unifies secrecy analysis of several classical models, thereby exhibiting enormous versatility than the existing works.

cs.IT

Strong coupling antiferromagnetic resonance with sub-THz cavity fields

Strong coupling of electromagnetic cavity fields with antiferromagnetic spin waves in hematite ($α$-Fe$_2$O$_3$) was achieved above room temperature. A cube of hematite was placed in a metallic tube and transmission was measured, using a continuous-wave THz spectrometer. Spectra, collected as a function of temperature, reveal the formation of magnetic polaritons.

cond-mat.mes-hall

Financial Crime & Fraud Detection Using Graph Computing: Application Considerations & Outlook

In recent years, the unprecedented growth in digital payments fueled consequential changes in fraud and financial crimes. In this new landscape, traditional fraud detection approaches such as rule-based engines have largely become ineffective. AI and machine learning solutions using graph computing principles have gained significant interest. Graph neural networks and emerging adaptive solutions provide compelling opportunities for the future of fraud and financial crime detection. However, implementing the graph-based solutions in financial transaction processing systems has brought numerous obstacles and application considerations to light. In this paper, we overview the latest trends in the financial crimes landscape and discuss the implementation difficulties current and emerging graph solutions face. We argue that the application demands and implementation challenges provide key insights in developing effective solutions.

cs.LG

Superconductivity at ~70 K in Tin Hydride SnHx under High Pressure

Various tin hydrides SnHx (x = 4, 8, 12, 14) have been theoretically predicted to be stable at high pressures and to show high-critical-temperature superconductivity with Tc ranging from about 70 to 100 K. However, experimental verifications for any of these phases are still lacking to date. Here, we report on the in-situ synthesis, electrical resistance, and synchrotron x-ray diffraction measurements of SnHx at ~ 200 GPa. The main phase of the obtained sample can be indexed with the monoclinic C2/m SnH12 via comparison with the theoretical structural modes. A sudden drop of resistance and the systematic downward shift under external magnetic fields signals the occurrence of superconductivity in SnHx at Tc = ~ 70 K with an upper critical field u0Hc2(0) = ~ 11.2 T, which is relatively low in comparison with other reported high-Tc superhydrides. Various characteristic superconducting parameters are estimated based on the BCS theory.

cond-mat.supr-con

Two-magnon frequency-pulling effect in ferromagnetic resonance

We report the experimental observation in thin films of the hybridization of the uniform ferromagnetic resonance mode with nonuniform magnons as a result of the two-magnon scattering mechanism, leading to a frequency-pulling effect on the ferromagnetic resonance. This effect, when not properly accounted for, leads to a discrepancy in the dependence of the ferromagnetic resonance field on frequency for different field orientations. The frequency-pulling effect is the complement of the broadening of the ferromagnetic resonance lineshape by two-magnon scattering and can be calculated using the same parameters. By accounting for the two-magnon frequency shifts through these means, consistency is achieved in fitting data from in-plane and perpendicular-to-plane resonance conditions.

cond-mat.mtrl-sci

Nanoscale lattice strains in self-ion implanted tungsten

Developing a comprehensive understanding of the modification of material properties by neutron irradiation is important for the design of future fission and fusion power reactors. Self-ion implantation is commonly used to mimic neutron irradiation damage, however an interesting question concerns the effect of ion energy on the resulting damage structures. The reduction in the thickness of the implanted layer as the implantation energy is reduced results in the significant quandary: Does one attempt to match the primary knock-on atom energy produced during neutron irradiation or implant at a much higher energy, such that a thicker damage layer is produced? Here we address this question by measuring the full strain tensor for two ion implantation energies, 2 MeV and 20 MeV in self-ion implanted tungsten, a critical material for the first wall and divertor of fusion reactors. A comparison of 2 MeV and 20 MeV implanted samples is shown to result in similar lattice swelling. Multi-reflection Bragg coherent diffractive imaging (MBCDI) shows that implantation induced strain is in fact heterogeneous at the nanoscale, suggesting that there is a non-uniform distribution of defects, an observation that is not fully captured by micro-beam Laue diffraction. At the surface, MBCDI and high-resolution electron back-scattered diffraction (HR-EBSD) strain measurements agree quite well in terms of this clustering/non-uniformity of the strain distribution. However, MBCDI reveals that the heterogeneity at greater depths in the sample is much larger than at the surface. This combination of techniques provides a powerful method for detailed investigation of the microstructural damage caused by ion bombardment, and more generally of strain related phenomena in microvolumes that are inaccessible via any other technique.

cond-mat.mtrl-sci

Reply to "Rapid $^{14}$C excursion at 3372-3371 BCE not observed at two different locations"

The nuclide $^{14}$C can be produced in the atmosphere by high energy particles and $γ$-rays from high-energy phenomena. Through the carbon cycle, some of $^{14}$CO$_2$ produced in the atmosphere can be retained in annual tree rings. Four events of rapid increase of the $^{14}$C content occurred in AD 775, AD 994, BC 660 and BC 3371 were found. Recently, the data of Jull et al. (2020) was inconsistent with our records around BC 3371. We measured our sample again and found the $^{14}$C records are consistent with the value in Wang et al. (2017). Therefore, our $^{14}$C records are robust. The inconsistency may be caused by the difference of calendar ages for the wood samples, or the physical origin of the event. First, crossdating on ring width can be performed only between trees whose growth has the same environmental conditions. Because the master tree-ring for dendrochronology is lack for Chinese trees. The master tree-ring from California has to be used. Therefore, the calendar ages derived from dendrochronology may be not precise. Second, the $^{14}$C even may be not global. One evidence is the variation of $^{14}$C content around AD 1006. The $^{14}$C contents of Californian trees increase 12\textperthousand~ in two years, while Japanese trees show no $^{14}$C increase.

astro-ph.SR

Autonomous Driving at Intersections: A Critical-Turning-Point Approach for Left Turns

Left-turn planning is one of the formidable challenges for autonomous vehicles, especially at unsignalized intersections due to the unknown intentions of oncoming vehicles. This paper addresses the challenge by proposing a critical turning point (CTP) based hierarchical planning approach. This includes a high-level candidate path generator and a low-level partially observable Markov decision process (POMDP) based planner. The proposed (CTP) concept, inspired by human-driving behaviors at intersections, aims to increase the computational efficiency of the low-level planner and to enable human-friendly autonomous driving. The POMDP based low-level planner takes unknown intentions of oncoming vehicles into considerations to perform less conservative yet safe actions. With proper integration, the proposed hierarchical approach is capable of achieving safe planning results with high commute efficiency at unsignalized intersections in real time.

cs.RO

Broad-lined type Ic supernova iPTF16asu: A challenge to all popular models

It is well-known that ordinary supernovae (SNe) are powered by 56Ni cascade decay. Broad-lined type Ic SNe (SNe Ic-BL) are a subclass of SNe that are not all exclusively powered by 56Ni decay. It was suggested that some SNe Ic-BL are powered by magnetar spin-down. iPTF16asu is a peculiar broad-lined type Ic supernova discovered by the intermediate Palomar Transient Factory. With a rest-frame rise time of only 4 days, iPTF16asu challenges the existing popular models, for example, the radioactive heating (56Ni-only) and the magnetar+56Ni models. Here we show that this rapid rise could be attributed to interaction between the SN ejecta and a pre-existing circumstellar medium ejected by the progenitor during its final stages of evolution, while the late-time light curve can be better explained by energy input from a rapidly spinning magnetar. This model is a natural extension to the previous magnetar model. The mass-loss rate of the progenitor and ejecta mass are consistent with a progenitor that experienced a common envelope evolution in a binary. An alternative model for the early rapid rise of the light curve is the cooling of a shock propagating into an extended envelope of the progenitor. It is difficult at this stage to tell which model (interaction+magnetar+56Ni or cooling+magnetar+56Ni) is better for iPTF16asu. However, it is worth noting that the inferred envelope mass in the cooling+magnetar+56Ni is very high.

astro-ph.HE

Probing nucleon's spin structures with polarized Drell-Yan in the Fermilab SpinQuest experiment

Although the proton was discovered about 100 years ago, its spin structure still remains a mystery. Recent studies suggest that the orbital angular momentum of sea quarks could significantly contribute to the proton's spin. The SeaQuest experiment, which recently completed data collection, probed the unpolarized light quark sea distributions of the proton using the Drell-Yan process. Its successor, the SpinQuest (E1039), will access the $\bar{u}$ and $\bar{d}$ Sivers functions using polarized NH$_3$ and ND$_3$ targets. A non-zero Sivers asymmetry, observed in SpinQuest, would be a strong indication of non-zero sea-quark orbital angular momentum. The SpinQuest experiment can also probe the sea quark's transversity distribution, which is relevant for the determination of proton's tensor charge. Recent study suggests that sea-quarks might contribute significantly to deuteron's tensor polarized structure functions. This can be further probed in SpinQuest using tensor polarized ND$_3$ target. The current status and future plan of the experiment are presented.

nucl-ex

Sub-Hertz Optomechanically-Induced Transparency

Optical interferometers with suspended mirrors are the archetype of all current audio-frequency gravitational-wave detectors. The radiation pressure interaction between the motion of the mirror and the circulating optical field in such interferometers represents a pristine form of light-matter coupling, largely due to 30 years of effort in developing high quality optical materials with low mechanical dissipation. However, in all current suspended interferometers, the radiation pressure interaction is too weak to be useful as a resource, and too strong to be neglected. Here, we demonstrate a meter-long interferometer with suspended mirrors, of effective mass $~ 125$ g, where the radiation pressure interaction is enhanced by strong optical pumping to realize a cooperativity of $50$. We probe this regime by observing optomechanically-induced transparency of a weak on-resonant probe. The low resonant frequency and high-Q of the mechanical oscillator allows us to demonstrate transparency windows barely $100$ mHz wide at room temperature. Together with a near-unity ($\sim 99.9\%$) out-coupling efficiency, our system saturates the theoretical delay-bandwidth product, rendering it an optical buffer capable of seconds-long storage times.

physics.optics

Testing Weak Equivalence Principle with Strongly Lensed Cosmic Transients

Current constraints on Einstein's weak equivalence principle (WEP) utilize the observed time delay between correlated particles of astronomical sources. However, the intrinsic time delay due to particle emission time is impossible to measure and is simply assumed to be zero in previous studies. Here we propose a robust method to test WEP for relativistic messengers using strongly lensed cosmic transients, which can naturally overcome the intrinsic time delay problem. This can be achieved in two ways: by comparing the time delays between lensed images seen in different energy bands or in gravitational waves (GWs) and their electromagnetic (EM) counterparts. The power of our method mainly depends on the timing accuracy of cosmic transient and the strong lensing time delay. If the time delay of cosmic transient can be measured with accuracy about 0.1 s (e.g. gamma-ray bursts), we show that the upper limit on the differences of the parameterized post-Newtonian parameter $γ$ value is $Δγ<10^{-7}$ with a one-month strong lensing time delay event. This accuracy of WEP can be improved by a factor of $10^{7}$, if the lens is galaxy cluster and the strongly lensed cosmic transients have much shorter duration, such as fast radio bursts.

astro-ph.HE

A New Method to Test the Einstein's Weak Equivalence Principle

The Einstein's weak equivalence principle (WEP) is one of the foundational assumptions of general relativity and some other gravity theories. In the theory of parametrized post-Newtonian (PPN), the difference between the PPN parameters $γ$ of different particles or the same type of particle with different energies, $Δγ$, represents the violation of WEP. Current constraints on $Δγ$ are derived from the observed time delay between correlated particles of astronomical sources. However, the observed time delay is contaminated by other effects, such as the time delays due to different particle emission times, the potential Lorentz invariance violation and none-zero photon rest mass. Therefore, current constraints are only upper limits. Here we propose a new method to test WEP based on the fact that the gravitational time delay is direction-dependent while others are not. This is the first method which can naturally correct other time delay effects. Using the time delay measurements of BASTE gamma-ray burst (GRB) sample and the gravitational potential of local super galaxy cluster Laniakea, we find that the constraint on $Δγ$ of different energy photons can be as low as $10^{-14}$. In the future, if more gravitational wave events and fast radio bursts with much more precise time delay measurements are observed, this method can give a reliable and tight constraint on WEP.

astro-ph.HE

Shaken Snow Globes: Kinematic Tracers of the Multiphase Condensation Cascade in Massive Galaxies, Groups, and Clusters

We propose a novel method to constrain turbulence and bulk motions in massive galaxies, groups and clusters, exploring both simulations and observations. As emerged in the recent picture of the top-down multiphase condensation, the hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (10^7 K) are perturbed by subsonic turbulence, warm (10^4 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (< 100 K) raining in the core via chaotic cold accretion (CCA). We show all phases are tightly linked via the ensemble (wide-aperture) velocity dispersion along the line of sight. The correlation arises in complementary long-term AGN feedback simulations and high-resolution CCA runs, and is corroborated by the combined Hitomi and new IFU measurements in Perseus cluster. The ensemble multiphase gas distributions are characterized by substantial spectral line broadening (100-200 km/s) with mild line shift. On the other hand, pencil-beam detections sample the small-scale clouds displaying smaller broadening and significant line shift up to several 100 km/s, with increased scatter due to the turbulence intermittency. We present new ensemble sigma_v of the warm Halpha+[NII] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). We show the physically motivated criterion C = t_cool/t_eddy ~ 1 best traces the condensation extent region and presence of multiphase gas in observed clusters/groups. The ensemble method can be applied to many available datasets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.

astro-ph.GA

A rapid cosmic-ray increase in BC 3372-3371 from ancient buried tree rings in China

Cosmic rays interact with the Earth's atmosphere to produce $^{14}$C, which can be absorbed by trees. Therefore, rapid increases of $^{14}$C in tree rings can be used to probe previous cosmic-ray events. By this method, three $^{14}$C rapidly increasing events have been found. Plausible causes of these events include large solar proton events, supernovae or short gamma-ray bursts. However, due to the lack of measurements of $^{14}$C by year, the occurrence frequency of such $^{14}$C rapidly increasing events is poorly known. In addition, rapid increases may be hidden in the IntCal13 data with five-year resolution. Here we report the result of $^{14}$C measurements using an ancient buried tree during the period between BC 3388 and 3358. We find a rapid increase of about 9\textperthousand~ in the $^{14}$C content from BC 3372 to BC 3371. We suggest that this event could originate from a large solar proton event.

astro-ph.HE