Millimeters In Direction Research Articles

KF-LSTM Based Beam Tracking for UAV-Assisted mmWave HSR Wireless Networks

Owing to the deployment flexibility, unmanned aerial vehicles (UAVs), equipped with lightweight base stations (BSs), provide a new paradigm for wireless access from the sky to temporarily complement terrestrial networks, which bring benefits to many applications, such high-speed railway (HSR) communications. In UAV-assisted wireless communications, the advantage of the line of sight (LOS) dominant air-ground channels makes it more attractive to apply directional millimeter wave (mmWave) communications, where beam management is highly related to user location. Nevertheless, due to the high mobility of UAVs and trains, how to accurately and efficiently track beams becomes a critical problem to solve. Based on this observation, in this paper, we first present an UAV-assisted dual-band HSR wireless network architecture, which integrates the frequency bands below 6 GHz (sub-6 GHz) to provide reliable transmissions for UAV controls and HSR safety services, with the mmWave bands to enhance the transmission capacity between UAVs and trains. To solve the beam tracking problem, we analyze the beam angular variations, and then propose an efficient algorithm based on Kalman filtering (KF) with varying update periods and long-short term memory (LSTM) to improve the beam tracking performance. Finally, we conduct extensive simulations to demonstrate that the proposed scheme can achieve more accurate beam tracking and higher spectrum efficiency.

Dependability of Directional Millimeter Wave Vehicle-to-Infrastructure Communications

Vehicle-to-infrastructure (V2I) communication is an important enabler for intelligent transportation and rail traffic management systems, which are expected to provide significant road traffic safety and efficiency enhancements. Such systems require a level of dependability of the wireless communication link that can be hard to support by state-of-the-art technologies. Transmissions in the millimeter wave (mmWave) band have the potential to provide sufficient bandwidth to support not only traffic management services, but additionally also web and entertainment applications for car and train passengers. mmWave transmissions require directional antennas at the transmitter and/or receiver to compensate for the significant pathloss and to achieve a practically acceptable maximum coupling loss. Such directional communication is feasible in V2I scenarios, because the mobility of users is confined to streets and roads. In this article, we discuss the dependability of directional mmWave V2I communications under two-ray fading conditions. We review methods for enhancing the dependability of the communication link by exploiting macroscopic spatial diversity and by mitigating interference from other transmitters. We furthermore provide guidelines for a dependable system design under two-ray fading and identify open research questions in this context.

Joint Routing and Resource Allocation for Millimeter Wave Picocellular Backhaul

Picocellular architectures are essential for providing the spatial reuse required to satisfy the ever-increasing demand for mobile data. A key deployment challenge is to provide backhaul connections with sufficiently high data rate. Providing wired support (e.g., using optical fiber) to pico base stations deployed opportunistically on lampposts and rooftops is impractical, hence wireless backhaul becomes an attractive approach. A multihop mesh network comprised of directional millimeter (mm) wave links is considered here for this purpose. Such networks are well suited for scaling backhaul data rates due to the abundance of spectrum in the mm wave bands, and the ability to form highly directional, electronically steerable beams. The backhaul design problem is formulated as one of joint routing and resource allocation, accounting for mutual interference across simultaneously active links. A computationally tractable formulation is developed by leveraging the localized nature of interference and the provable existence of a sparse optimal allocation. Numerical results are provided for topologies modeling urban and suburban settings.

Perforation Optimization of DMFC Anode Porous Medium

Carbon Dioxide management is essential to the development of Direct Methanol Fuel Cell Anode. CO2 bubbles evolution at the anode can create large mass transport loss and block the sites where the triple phase boundary occurs for the electrochemical reaction. The gas can be trapped in the Gas diffusion layer (GDL) and block the channels from the incoming fuel [1-2]. Researchers have studied the mechanism and the dynamics by visualizations of how CO2 bubbles evolve from the catalyst layers [3-5]. Some studies have been done to the anode structure to improve the performances by modifying the material, wettability, porosity and thickness [6-8]. However, disagreements have been confirmed from different design aspects to whether those modifications reduce the mass transport loss or not [9-11]. In this study, pathways/perforations were created by laser perforating the Gas Diffusion layer (GDL) to enhance the mass transport from and to the catalyst layer. Results have shown superiority of the perforated GDL over the conventional GDL. Further optimization of the perforation diameter, the spacing along the lateral and channel directions have been accomplished. First, the perforation diameter size was investigated with minimum number of holes, 16 holes, spaced with 2 millimeters in lateral and channel directions over the 1 cm^2 active area of the electrode, as can be seen in Figure 1A. The 60-micron diameter showed little improvement over the virgin GDL while further increase of the diameter caused massive mass transport loss. Secondly, further optimization of the spacing in the lateral and channel directions in Figure 1B, it was found that the 60-micron diameter with 1 millimeter in lateral spacing and 2 millimeter in channel spacing increased the maximum power density by roughly 30% compared to virgin GDL. Figure1: A) Different perforation diameter ranging from 60-500 micron with 16 holes; B) Spacing optimization in lateral and channel directions. Figure 1

Antenna-assisted subwavelength metal–InGaAs–metal structure for sensitive and direct photodetection of millimeter and terahertz waves

Millimeter and terahertz wave photodetectors have a wide range of applications. However, the state-of-the-art techniques lag far behind the urgent demand due to the structure and performance limitations. Here, we report sensitive and direct millimeter and terahertz wave photodetection in compact InGaAs-based subwavelength ohmic metal–semiconductor–metal structures. The photoresponse originates from unidirectional transportation of nonequilibrium electrons induced by surface plasmon polaritons under irradiation. The detected quantum energies of electromagnetic waves are far below the bandgap of InGaAs, offering, to the best of our knowledge, a novel direct photoelectric conversion pathway for InGaAs beyond its bandgap limit. The achieved room temperature rise time and noise equivalent power of the detector are 45 μs and 20 pW·Hz−1/2, respectively, at the 0.0375 THz (8 mm) wave. The detected wavelength is tunable by mounting different coupling antennas. Room temperature terahertz imaging of macroscopic samples at around 0.166 THz is also demonstrated. This work opens an avenue for sensitive and large-area uncooled millimeter and terahertz focal planar arrays.

Indoor wideband directional millimeter wave channel measurements and analysis at 26 GHz, 32 GHz, and 39 GHz

AbstractThis paper presents details of the wideband directional propagation measurements of millimeter‐wave (mmWave) channels in the 26 GHz, 32 GHz, and 39 GHz frequency bands in an indoor typical office environment. More than 14 400 power delay profiles (PDPs) were measured across the 26 GHz band and over 9000 power delay profiles have been recorded for the 32 GHz and 39 GHz bands at each measurement point. A mmWave wideband channel sounder has been used, where signal analyzer and vector signal generator were employed. Measurements have been conducted for both co and cross‐antenna polarization. The setup provided 2 GHz bandwidth and the mechanically steerable directional horn antenna with 8 degrees beamwidth provides 8 degrees of directional resolution over the azimuth for 32 GHz and 39 GHz, whereas 26 GHz measurement setup provides the angular resolution of 5 degrees. Measurements provide path loss, delay, and spatial spread of the channel. Large‐scale fading characteristics, RMS delay spread, RMS angular spread, and angular and delay dispersion are presented for 3 mmWave bands for the line‐of‐sight scenario.

Application of toluene LIF to transonic nozzle flows to identify zones of incomplete molecular mixing.

Toluene laser-induced fluorescence (LIF) has been applied to image the mixing deficit on the molecular level in the transonic wake of two different blunt-body injectors in a compressible accelerated nozzle flow. A single-color excitation and two-color detection scheme is employed to measure the signal red-shift caused by the quenching effect of molecular oxygen on the fluorescence of toluene, which reduces and red-shifts the LIF signal if both substances interact on a molecular level. To this end, toluene is injected alternatingly with O2-contaning and O2-free carrier gas into the air main flow. Differences of both signals mark regions where mixing on molecular level is incomplete. A zone of molecular mixing deficit extending several millimeters in stream-wise direction is identified. The effect of local variations in temperature on the sensitivity of this technique is discussed using photo-physical data measured in a stationary low-temperature cell.

Double Directional Millimeter Wave Propagation Channel Measurement and Polarimetric Cluster Properties in Outdoor Urban Pico-cell Environment

Double Directional Millimeter Wave Propagation Channel Measurement and Polarimetric Cluster Properties in Outdoor Urban Pico-cell Environment

Enabling UAV cellular with millimeter-wave communication: potentials and approaches

To support high data rate urgent or ad hoc communications, we consider mmWave UAV cellular networks and the associated challenges and solutions. To enable fast beamforming training and tracking, we first investigate a hierarchical structure of beamforming codebooks and design of hierarchical codebooks with different beam widths via the sub-array techniques. We next examine the Doppler effect as a result of UAV movement and find that the Doppler effect may not be catastrophic when high gain directional transmission is used. We further explore the use of millimeter wave spatial division multiple access and demonstrate its clear advantage in improving the cellular network capacity. We also explore different ways of dealing with signal blockage and point out that possible adaptive UAV cruising algorithms would be necessary to counteract signal blockage. Finally, we identify a close relationship between UAV positioning and directional millimeter wave user discovery, where update of the former may directly impact the latter and vice versa.

Electrical switching of magnetization in a layer of α-Fe with a naturally hydroxidized surface

It is well established that electrical methods, such as the application of a high-density (1010–1011 A m−2) current, can be employed for the switching of magnetization in thin ferromagnetic films and heterostructures after their patterning at the nanoscale. We find that magnetization is robustly switchable, i.e., at macroscopic scales (up to a few millimeters in lateral directions), in a single ∼30 nm-thick layer of α-Fe upon discharging a capacitor through the sample. Interestingly, samples sputtered at enhanced base pressures (∼10−6 mbar) exhibited much lower switching thresholds with no bias field, while their electrical conductivity is anomalously high (higher than that in bulk of α-Fe). We argue that the observed enhancement of conduction relates to the mixed oxide/oxyhydroxide (FeO/FeOOH) layer formed naturally on the top of our α-Fe films. This provides an explanation for the magnetization switching upon discharging a capacitor in terms of the Oersted field generated by the discharge current. We analyze the ratio needed between the conductions of the FeO/FeOOH layer and the underlying α-Fe for the effective action of the Oersted field.

Temporal and spatial properties of a yeast multi-cellular amplification system based on signal molecule diffusion.

We report on the spatial and temporal signaling properties of a yeast pheromone-based cell communication and amplifier system. It utilizes the Saccharomyces cerevisiae mating response pathway and relies on diffusion of the pheromone α–factor as key signaling molecule between two cell types. One cell type represents the α–factor secreting sensor part and the other the reporter part emitting fluorescence upon activation. Although multi-cellular signaling systems promise higher specificity and modularity, the complex interaction of the cells makes prediction of sensor performance difficult. To test the maximum distance and response time between sensor and reporter cells, the two cell types were spatially separated in defined compartments of agarose hydrogel (5 × 5 mm) and reconnected by diffusion of the yeast pheromone. Different ratios of sensor to reporter cells were tested to evaluate the minimum amount of sensor cells required for signal transduction. Even the smallest ratio, one α–factor-secreting cell to twenty reporter cells, generated a distinct fluorescence signal. When using a 1:1 ratio, the secreted pheromone induced fluorescence in a distance of up to four millimeters after six hours. We conclude from both our experimental results and a mathematical diffusion model that in our approach: (1) the maximum dimension of separated compartments should not exceed five millimeters in gradient direction; and (2) the time-limiting step is not diffusion of the signaling molecule but production of the reporter protein.

Scanning tunneling microscope with long range lateral motion

We present our work on a recently built scanning tunneling microscope (STM), with coarse motion in two-dimensions. The tip of this STM can be translated a few millimeters in directions both parallel and perpendicular to the tip. This feature allows sampling of a larger area for experiments such as the study of how the electrical properties of charge density waves evolve between contacts, the proximity effect near a normal metal–superconducting interface, charge transport near the contact of a semiconductor interface, and for finding microscopically small samples like graphene. This STM is based on one of our previous one-dimensional designs. It utilizes orchestrated motion of six piezoelectric tubes in a slip–stick configuration in order to produce long range motion for the walker. This device is a single unit with a compact design making it very stable. It is stable enough to obtain atomic resolution on HOPG. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures. It was designed entirely from non-magnetic materials for potential work in a magnetic field.

Comparison Between Quantification Methods of Carotid Artery Stenosis and Computed Tomographic Angiography

The purpose of this study was to compare 3 percentage carotid artery measurement methods (the North American Symptomatic Carotid Endarterectomy Trial [NASCET], the European Carotid Surgery Trial [ECST], and the Carotid Stenosis Index [CSI]) and 1 millimeter method (direct millimeter measurement) to evaluate the difference and correlation between them. Seven hundred ninety-two patients (591 men; age: mean, 63 years; range, 32-91 years) studied by using a multi-detector row computed tomographic scanner for a total of 1584 carotid arteries were retrospectively analyzed. Each carotid stenosis was measured according to 4 measurement methods (the NASCET, the ECST, the CSI, and the direct millimeter measurement). Carotid arteries with near-occlusion condition were excluded. The Kolmogorov-Smirnov Z test was used to test the normality of continuous variable groups. Comparison of derived ratio-percent methods was performed by using the Bland-Altman plots, and receiver operating characteristic curves were calculated. Correlation coefficients were also calculated by using a nonparametric Spearman correlation. A P < 0.05 was considered to mean statistical significance. Four hundred sixteen carotid arteries were excluded, and in the remaining 1168 ones, a strength correlation according to quadratic regression between the NASCET and ECST methods was observed (Spearman rho coefficient, 0.948; P < 0.0001). An inverse correlation according to linear regression was observed between the NASCET and the direct millimeter measurement (Spearman rho coefficient, -0.972; P < 0.0001); the CSI shows a quadratic regression with the NASCET, a linear regression with the ECST, and an inverse linear regression with the direct millimeter measurement (Spearman rho coefficient, 0.946, 0.932, and -0.939 respectively). The cutoff values for 50% and 70% NASCET stenosis were 2.36 and 1.51, respectively. Our study results indicate that the direct millimeter measurement of stenosis, by using appropriate equations, can reliably predict NASCET-, ECST-, and CSI-type percent stenoses. The use of direct millimeter measurement may remove the pitfalls and the discrepancies deriving from the use of different ratio-percent methods.

Classification of Carotid Stenosis by Millimeter CT Angiography Measures: Effects of Prevalence and Gender

Previous studies quantifying moderate and severe carotid stenosis by direct millimeter measures on CT angiography (CTA) did not consider how prevalence and gender may influence classification cutoff values. Three hundred nineteen carotid arteries were evaluated in consecutive patients with known or suspected carotid artery disease. Millimeter measures were obtained of the stenotic carotid bulb lumen and distal internal carotid artery (ICA). Interclass correlation coefficients (ICC) defined interobserver and intraobserver agreement. North American Symptomatic Carotid Endarterectomy Trial (NASCET)-style percent stenosis ratios were calculated per carotid artery and used in linear regression and receiver operating characteristic (ROC) curve analysis to define equivalent millimeter quantification and classification values. Likelihood ratios and prevalence-specific positive/negative predictive values (PPV/NPV) were calculated to determine the most appropriate millimeter cutoff values to classify stenosis. Interobserver agreement was excellent for stenosis measures (0.90) and good for distal ICA measures (0.79). Gender-specific regression curves and ROC curves indicated that millimeter stenosis is an excellent tool to quantify and classify carotid stenosis. Assuming a 10% prevalence of severe stenosis, we found that the cutoff value maximizing NPV and PPV was 1.1 mm for both genders (female: PPV = 86.2, NPV = 97.7; male: PPV = 83.2, NPV = 95.9). Assuming a 40% prevalence of moderate stenosis, we found that the cutoff values differed between genders: female = 2.0 mm (PPV = 91.3, NPV = 91.5), male = 2.1 mm (PPV = 91.6, NPV = 92.4). Specific millimeter cutoffs will vary depending upon the clinical scenario, prevalence, and gender. Direct millimeter stenosis measures are an excellent tool to classify moderate and severe carotid artery stenosis. Millimeter classification cutoff values that best approximate NASCET classifications vary depending on prevalence and gender.

Pattern and pharmacology of propagating epileptiform activity in mouse cerebral cortex.

Multiple extracellular recording electrodes were used to study the intra- and interhemispheric spread of stimulus-evoked epileptiform responses in adult mouse neocortical slices. Bath application of 20 microM bicuculline methiodide induced epileptiform activity that propagated at approximately 0.08 m/s over several millimeters in rostro-caudal and medio-lateral direction within the ipsilateral hemisphere and across the corpus callosum to the contralateral hemisphere. A vertical incision from layer II to subcortical regions did not prevent the spread to remote cortical regions, indicating that layer I plays a major role in the lateral propagation of epileptiform activity. The intra- and interhemispheric spread was not influenced by application of an N-methyl-d-aspartate (NMDA) receptor antagonist, but blocked by an antagonist acting at the (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-type glutamate receptor. The potential role of potassium channel activation in controlling the generation or spread of epileptiform activity was tested by applying the potassium channel opener cromakalim and the serotonin type 1A (5-HT1A) receptor agonist (+/-)-8-hydroxydipropylaminotetralin (8-OH-DPAT) to the disinhibited slices. Whereas cromakalim reduced the neuronal excitability and blocked all epileptiform responses, 8-OH-DAPT did not affect the activity pattern. Our results suggest that propagating epileptiform activity in disinhibited neocortical structures is predominantly mediated by activation of AMPA receptors and controllable by activation of a voltage-dependent potassium current.