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Designing a robot with the best accuracy is always the attractive research direction in robot community. In order to create a Gough-Stewart platform with guaranteed accuracy performance for a dedicated controller, this paper describes a novel advanced optimal design methodology: control-based design methodology. This advanced optimal design method considers the controller positioning accuracy in the design process for getting the optimal geometric parameters of the robot. In this paper, three types of visual servoing controllers are applied to control the motions of the Gough-Stewart platform: leg-direction-based visual servoing, line-based visual servoing and image moment visual servoing. Depend on these controllers, the positioning error models considering the camera observation error together with the controller singularities are analyzed. In the next step, the optimization problems are formulated in order to get the optimal geometric parameters of the robot and the placement of the camera for the Gough-Stewart platform for each type of controller. Then, we perform the co-simulations on the three optimized Gough-Stewart platforms in order to test the positioning accuracy and the robustness with respect to the manufacturing errors. It turns out that the optimal control-based design methodology helps getting both the optimum design parameters of the robot and the performance of the controller {robot + dedicated controller}.

Objective Regional homogeneity (ReHo) differences in encephalic regions of Parkinson’s disease (PD) patients of different subtypes were investigated to analyze its clinical significance during disease occurrence. Methods 39 PD patients were evaluated in this study, which included 14 cases with the tremor dominant (TD) PD subtype and 23 cases with the postural instability and gait difficulty (PIGD) PD subtype, along with 28 healthy individuals, who were included as the control group. Magnetic resonance imaging (MRI) was performed for all the cases to obtain the rest-state functional magnetic resonance imaging (R-fMRI) data along with structural data. The ReHo values of the three groups were calculated and disparities in brain structures among the three groups were processed by analysis of variance. In addition, t-test analysis was used to evaluate the differences between the groups. In the end, a correlation analysis between the brain areas evaluated for ReHo differences and the clinical symptoms presented by the patients was carried out. Results Compared to the control group, brain areas with increased ReHo values in the TD PD subtype group, included the right putamen, right para-hippocampal gyrus, right inferior temporal gyrus, and right orbital superior frontal gyrus, while areas with decreased ReHo values, included the bilateral superior occipital gyrus and bilateral middle occipital gyrus. In contrast with the control group, areas like the right putamen, right superior temporal gyrus, left thalamus, and right superior parietal gyrus in the PIGD PD subtype group presented an increased in ReHo values, while a decreased in ReHo values was found in the right para-hippocampal gyrus, bilateral superior occipital gyrus, and middle occipital gyrus. Compared to the PIGD group, the TD group showed an increase in ReHo values in the right para-hippocampal gyrus. Conclusions In the present study, ReHo values increased in the TD PD subtype group of patients, indicating a compensatory performance of slow progressive cognitive decline when compared to the PIGD PD subtype group. Two subtypes of PD manifest ReHo changes in the basal ganglia, thalamus, and in several areas of the cerebral cortex, areas that are likely to correlate with non-motor symptoms, such as cognition and emotions.

Background: Previous studies had compared the effectiveness of surgical and conservative treatment in proximal humeral fracture (PHF), suggesting that both treatments were effective for displaced fractures. However, which treatment is more effective, especially in the elderly patient population, remains controversial to date. This study aims to evaluate the efficacy of the two treatment methods, including functional outcome scores, complications, etc.Methods: We searched four databases (MEDLINE, Web of Science, EMBASE, Cochrane Library) from the inception of the databases to March 2020. Within the scope of the search, the publication time and language of the relevant literatures were not limited. The meta-analysis directly compared the results and complications of the two groups and subgroups. Results: We included 11 comparative studies into our meta-analysis. The contents of the study included 7 randomized controlled trials (RCTs) and 4 non-randomized controlled trials (nRCTs). The pooled data demonstrated that there was no significant difference in postoperative Constant score between surgical and conservative treatment in the RCT subgroup, but there were differences among the nRCT and prosthesis subgroup. Although there was no significant difference between the surgery and conversation group in the major postoperative complications, the subgroup analysis showed fewer complications in the joint prosthesis replacement group. Conclusion: Both treatments could provide better clinical results for patients. The joint prosthesis replacement may offer additional benefits in terms of reduced complications and postoperative function. Furthermore, due to the increasing number of prosthesis replacements and the advent of the aging age, we should consider the individual differences between patients and enrich the clinical efficacy through the personal experience of surgeons before choosing treatment options.

Background: Gait impairments including shuffling gait and hesitation are common in people with Parkinson's disease (PD), and have been linked to increased fall risk and freezing of gait. Nowadays the gait metrics mostly focus on the spatiotemporal characteristics of gait, but less is known of the angular characteristics of the gait, which may provide helpful information pertaining to the functional status and effects of the treatment in PD. Objective: This study aimed to quantify the angles of steps during walking, and explore if this novel step angle metric is associated with the severity of PD and the effects of the treatment including the acute levodopa challenge test (ALCT) and deep brain stimulation (DBS). Methods: A total of 18 participants with PD completed the walking test before and after the ALCT, and 25 participants with PD completed the test with the DBS on and off. The walking test was implemented under two conditions: walking normally at a preferred speed (single task) and walking while performing a cognitive serial subtraction task (dual task). A total of 17 age-matched participants without PD also completed this walking test. The angular velocity was measured using wearable sensors on each ankle, and three gait angular metrics were obtained, that is mean step angle, initial step angle, and last step angle. The conventional gait metrics (ie, step time and step number) were also calculated. Results: The results showed that compared to the control, the following three step angle metrics were significantly smaller in those with PD: mean step angle (F-1,F-48=69.75, P

We present γ-ray radiation detection in a neutron radiation environment using a monolithic active pixel sensor (MAPS) camera without conversion or shielding layers. The measured output signal is the sum of the pedestal value, noise, and real radiation response signal. The sensor response shows that the MAPS camera is sensitive to neutrons and can capture a single photon. The number of pixels with a signal exceeding 100 exhibits a strong dependence on the dose rate and is the best indicator of this value. Therefore, a MAPS camera can be efficiently used as a radiation detection sensor in a robotic system, further limiting human errors in performing radiation detection in complex nuclear radiation environments.

It is a significant but ignored issue to quantify the influence of Deep Brain Stimulation (DBS) surgery in patients with Parkinson's disease during the whole perioperative period. In this paper, wearable sensors were utilized to record patients' motor changes in the time before surgery, after surgery with stimulation off and stimulation on. The results showed that the DBS surgery is effective and safe in the perioperative period.

DeepLab v3+ neural network shows excellent performance in semantic segmentation. In this paper, we proposed a segmentation framework based on DeepLab v3+ neural network and applied it to the problem of hyperspectral imagery classification (HSIC). The dimensionality reduction of the hyperspectral image is performed using principal component analysis (PCA). DeepLab v3+ is used to extract spatial features, and those are fused with spectral features. A support vector machine (SVM) classifier is used for fitting and classification. Experimental results show that the framework proposed in this paper outperforms most traditional machine learning algorithms and deep-learning algorithms in hyperspectral imagery classification tasks.

Membrane gas absorption (MGA) based on ceramic membranes is considered to be an effective technology for removing SOx from ship exhaust. To develop a convenient method for designing and amplifying a membrane contactor, the critical gas velocity was defined. Two simple connection modes, series and parallel modules, were assembled and compared with a single-tube membrane contactor. The critical gas velocity is associated with the size of the membrane element and module, based on which an empirical equation can be formulated to optimize the gas velocity in different membrane contactors. In addition, another amplifying method, using multiple tubes in one shell, was also studied with computational fluid dynamics (CFD) simulations. The results imply that the addition of baffles improves the desulfurization performance of the membrane contactor at the critical gas velocity. The methods and conclusions presented herein provide a design basis for using the contactor at an industrial scale.

In wireless local area networks (WLANs), link-layer multicast is a promising technology for many multimedia applications, e.g., video streaming, as multicast frames can reach multiple clients simultaneously. However, the efficiency of multicast in WLANs is usually low since multicast frames are transmitted at a basic data rate to reach clients with poor channel quality. Moreover, the reliability of multicast cannot be guaranteed either, as multicast transmissions are not acknowledged. Some recent works have utilized smart antennas to improve multicast performance. However, most of them require customized hardware and are not designed for the latest IEEE 802.11 standard, 802.11n WLANs. More importantly, these works did not consider the impact of AP association strategies on the performance of link-layer multicast. In this paper, we study the problem of link-layer multicast in large-scale 802.11n WLANs where each AP is equipped with a smart antenna that supports multiple antenna patterns. Based on channel gains of various antenna patterns from different APs, we choose the associated AP for multicast clients, partition associated clients of each AP into multiple groups, select an antenna pattern and data rate for each group of client, and transmit multicast frames to each group once. We first examine the limitation of multicast in 802.11n WLANs and the benefits of smart antennas to multicast via experiments. We then introduce the system model and formulate the problem into an optimization problem, and prove its NP-hardness. The objective is to minimize the time to transmit a multicast frame to all clients while guaranteeing high packet reception ratio (PRR) for each client. For generic WLANs where APs are sparsely deployed, we propose an optimal algorithm under the condition that the PRR of antenna patterns and data rates are known for every client. For generic large-scale WLANs, we further propose an on-line algorithm in which the AP association strategy, the partition of clients, the antenna pattern and data rate of each group are adapted dynamically, based on PRR reports from clients. We have implemented the on-line algorithm on off-the-shelf WLAN products, and conducted extensive experiments and simulations to evaluate the performance. The results show that the proposed algorithm can significantly improve multicast performance compared to other schemes, and at the same time guarantee high PRR for all clients.

A considerable number of studies have been conducted to study the microbial profiles in inflammatory conditions. A common phenomenon in inflammatory bowel disease (IBD) is the reduction of the diversity of microbiota, which demonstrates that microbial diversity negatively correlates with disease severity in IBD. Increased microbial diversity is known to occur in disease remission. Species diversity plays an important role in maintaining the stability of the intestinal ecosystem as well as normal ecological function. A reduction in microbial diversity corresponds to a decrease in the stability of the ecosystem and can impair ecological function. Fecal microbiota transplantation (FMT), probiotics, and prebiotics, which aim to modulate the microbiota and restore its normal diversity, have been shown to be clinically efficacious. In this study, we hypothesized that a reduction in microbial diversity could play a role in the development of IBD.

The type of road terrain is an important piece of environment perception information for smart vehicles. In this paper, an approach to recognize the road terrain by using road surface images is proposed. The texture features were extracted from images captured by a camera for the road terrain classification task. The support vector machine method was selected for terrain classification. The simulation experiments indicated that this approach worked very well on terrains with distinguished texture. However, this approach could not recognize the road terrain when the damaged captured image changed frequently due to the luminance or when the moving speed of the vehicle was too fast.

Recent studies have shown that significant benefit can be achieved in wireless sensor networks (WSNs) by employing mobile collectors for data gathering via short-range communications. A typical scenario for such a scheme is that a mobile collector roams over the sensing field and pauses at some anchor points on its moving tour such that it can traverse the transmission range of all the sensors in the field and directly collect data from each sensor. In this paper, we study the performance optimization of such mobile data gathering by formulating it into a cost minimization problem constrained by channel capacity, required minimum data uploads from each sensor and bound of total sojourn time at all anchor points. In order to provide an efficient and distributed algorithm, we decompose this global optimization problem into two subproblems that can be solved by each sensor and the mobile collector, respectively. We show that such decomposition can be characterized as a pricing mechanism, in which each sensor independently adjusts its payment for the data uploading opportunity based on the shadow prices of different anchor points. Correspondingly, we give an efficient algorithm to jointly solve the two subproblems. Our theoretical analysis demonstrates that the proposed algorithm can achieve the optimal data control for each sensor and the optimal sojourn time allocation for the mobile collector, which minimizes the overall network cost. Finally, extensive simulation results further validate that our algorithm achieves lower cost than the compared data gathering strategy.

One of the motivations of OptoBot Lab is to train primer students into qualified engineers or researchers. The series training programs have been designed by supervisors and implemented with tutoring for students to test and practice their knowledge from textbooks. An environment perception experiment using a 32 layers laser scanner is described in this paper. The training program design and laboratory operation is introduced. The four parts of the experiments which are preparation, sensor calibration, 3D space reconstruction, and object recognition, are the participating students’ main tasks for different teams. This entire program is one of the series training programs that play significant role in establishing solid research skill foundation for opto-electronic students.

This study proposes an adaptive neural network controller for a 3-DOF robotic manipulator that is subject to backlash-like hysteresis and friction. Two neural networks are used to approximate the dynamics and the hysteresis non-linearity. A neural network, which utilises a radial basis function approximates the robot's dynamics. The other neural network, which employs a hyperbolic tangent activation function, is used to approximate the unknown backlash-like hysteresis. The authors also consider two cases: full state and output feedback control. For output feedback, where system states are unknown, a high gain observer is employed to estimate the states. The proposed controllers ensure the boundedness of the control signals. Simulations are also performed to show the effectiveness of the controllers.

Recently, several multi-channel MAC protocols have been proposed for wireless sensor networks (WSNs) to improve network capacity and boost energy efficiency. In addition, cooperative multiple-input multiple-output (MIMO) technique has been shown to be able to significantly enhance the energy efficiency of WSNs if properly configured. However, these two promising techniques have not been jointly considered in clustered WSNs. In this paper, we explore such a joint design by proposing a novel MAC protocol for clustered WSNs that takes advantage of both multiple channels and cooperative MIMO to further boost network performance. Specifically, sensor nodes in a WSN are organized into clusters and each cluster head selects some cooperative nodes to help forward traffic to or receive from other clusters by utilizing a cooperative MIMO technique. For intra-cluster communications, different channels are assigned to adjacent clusters to reduce collisions, while for inter-cluster communications, cooperative MIMO links are scheduled to improve energy efficiency and concurrent transmissions are enabled by assigning different channels to them. We also provide a network-wide time synchronization approach to facilitating the functionality of this protocol. We carry out extensive simulations and the results demonstrate that the proposed protocol can significantly increase throughput and improve energy efficiency compared to other schemes. For example, for a WSN with 150 sensors in a 250 i? 250 m 2 field, with five available channels, the protocol can achieve three times saturated throughput while saving 14 % energy per bit for inter-cluster communications. Propose a multi-channel, cooperative MIMO MAC protocol for clustered WSNs.Employ cooperative MIMO links for inter-cluster communications.Assign orthogonal channels to interfering cooperative links to boost throughput.Numerical results show that energy efficiency of WSNs is remarkably improved.Simulation results show that network throughput is significantly enhanced.

As the latest amendment of IEEE 802.11 standard, 802.11n allows a maximum raw data rate as high as 600 Mbps, making it a desirable candidate for wireless local area network (WLAN) deployment. In typical deployment, the coverage areas of nearby access points (APs) usually overlap with each other to provide satisfactory coverage and seamless mobility support. Clients tend to associate (connect) to the AP with the strongest signal strength, which may lead to poor client throughput and overloaded APs. Although a number of AP association schemes have been proposed for IEEE 802.11 WLANs in the literature, the challenges brought by the new features in 802.11n have not been thoroughly studied nor the impact of legacy 802.11a/b/g clients in 802.11n WLANS on AP association. To fill in this gap, in this paper, we explore AP association for 802.11n with heterogeneous clients (802.11a/b/g/n). We first present a bi-dimensional Markov model to estimate the uplink and downlink throughput of clients and formulate AP association into an optimization problem, aiming at providing each client a bandwidth proportional to its usable data rate. Based on this Markov model, we propose an on-line AP association algorithm under the condition that each client can acquire timely information of all clients associated with nearby APs. Furthermore, for WLANs with densely deployed APs, we provide another on-line AP association algorithm with lower complexity, which takes full advantage of 802.11n transmissions by simply associating different types of clients with different APs. We have conducted extensive simulations and experiments to validate the proposed algorithms. The results show that our algorithms can significantly improve both 802.11n throughput and aggregated network throughput under various network scenarios, compared to previous AP association schemes. Our experiments also confirm the effectiveness of the algorithms in enhancing network throughput, maintaining proportional fairness among clients, and balancing load among APs.

Data gathering is a fundamental operation in various applications of wireless sensor networks (WSNs), where sensor nodes sense information and forward data to a sink node via multi-hop wireless communications. Typically, data in a WSN is relayed over a tree topology to the sink for effective data gathering. A number of tree-based data gathering schemes have been proposed in the literature, most of which aim at maximizing network lifetime. However, the timeliness and reliability of gathered data are also of great importance to many applications in WSNs. To achieve low-latency, high-reliability data gathering in WSNs, in this paper, we construct a data gathering tree based on a reliability model, schedule data transmissions for the links on the tree and assign transmitting power to each link accordingly. Since the reliability of a link is highly related to its signal to interference plus noise ratio (SINR), the SINR of all the currently used links on the data gathering tree should be greater than a threshold to guarantee high reliability. We formulate the joint problem of tree construction, link scheduling and power assignment for data gathering into an optimization problem, with the objective of minimizing data gathering latency. We show the problem is NP-hard and divide the problem into two subproblems: Constructing a low-latency data gathering tree; Jointly link scheduling and power assignment for the data gathering tree. We then propose a polynomial heuristic algorithm for each subproblem and conduct extensive simulations to verify the effectiveness of the proposed algorithms. Our simulation results show that the proposed algorithms achieve much lower data gathering latency than existing data gathering strategies while guaranteeing high reliability. Moreover, the algorithms also have a comparable energy efficiency and network lifetime to other algorithms.

As the latest IEEE 802.11 standard, 802.11n applies several new technologies, such as multiple input multiple output (MIMO), channel bonding, and frame aggregation to greatly improve the rate, range and reliability of wireless local area networks (WLANs). In 802.11n WLANs, access points (APs) are often densely deployed to provide satisfactory coverage. Thus nearby APs should operate at non-overlapping channels to avoid mutual interference. It is challenging to assign channels in legacy 802.11a/b/g WLANs due to the limited number of channels. Channel assignment becomes more complex in 802.11n WLANs, as the channel bonding in 802.11n allows WLAN stations (APs and clients) to combine two adjacent, non-overlapping 20MHz channels together for transmission. On the other hand, IEEE 802.11n is backward compatible, such that 802.11n clients will coexist with legacy clients in 802.11n WLANs. Legacy clients may affect the performance of nearby 802.11n clients, and reduce the effectiveness of channel bonding. Based on these observations, in this paper, we study channel assignment in 802.11n WLANs with heterogeneous clients. We first present the network model, interference model, and throughput estimation model to estimate the throughput of each client. We then formulate the channel assignment problem into an optimization problem, with the objective of maximizing overall network throughput. Since the problem is NP-hard, we give a distributed channel assignment algorithm based on the throughput estimation model. We then present another channel assignment algorithm with lower complexity, and aim at minimizing interference experienced by high-rate, 802.11n clients. We have carried out extensive simulations to evaluate the proposed algorithms. Simulation results show that our algorithms can significantly improve the network throughput of 802.11n WLANs, compared with other channel assignment algorithms.

Recent experimental studies have revealed that a large percentage of wireless links are lossy and unreliable for data delivery in wireless sensor networks (WSNs). Such findings raise new challenges for the design of clustering algorithms in WSNs in terms of data reliability and energy efficiency. In this paper, we propose distributed clustering algorithms for lossy WSNs with a mobile collector, where the mobile collector moves close to each cluster head to receive data directly and then uploads collected data to the base station. We first consider constructing one-hop clusters in lossy WSNs where all cluster members are within the direct communication range of their cluster heads. We formulate the problem into an integer program, aiming at maximizing the network lifetime, which is defined as the number of rounds of data collection until the first node dies. We then prove that the problem is NP-hard. After that, we propose a metric-based distributed clustering algorithm to solve the problem. We adopt a metric called selection weight for each sensor node that indicates both link qualities around the node and its capability of being a cluster head. We further extend the algorithm to multi-hop clustering to achieve better scalability. We have found out that the performance of the one-hop clustering algorithm in small WSNs is very close to the optimal results obtained by mathematical tools. We have conducted extensive simulations for large WSNs and the results demonstrate that the proposed clustering algorithms can significantly improve the data reception ratio, reduce the total energy consumption in the network and prolong network lifetime compared to a typical distributed clustering algorithm, HEED, that does not consider lossy links.

In this paper, 850V breakdown voltage LDMOS fabricated on Simbond SOI wafer are reported. Simbond SOI wafers with 1.5@mm top silicon, 3@mm buried oxide layer, and n-type heavy doped handle wafers are used. In order to achieve uniform lateral electric field and shorten the vertical impact ionization integration path simultaneously, an optimized 60@mm drift region implant mask is designed to realize a linearly graded doping profile, and silicon thickness in the drift region is reduced from 1.5@mm to about 0.26@mm by thick field oxide process. CMOS compatible SOI LDMOS processes are designed and implemented successfully. Off-state breakdown voltage of SOI LDMOS can reach 850V, and the specific on-resistance is 56@Wmm^2. Experimental results also show the thickness of the top silicon in the drift region has a good uniformity. The performance of SOI LDMOS indicated that Simbond SOI wafers are good choice for thin film high voltage devices.

Synchrotron radiation x-ray reflectivity measurement is used to study the concentration profile of a delta-doped Er layer in Si epitaxial film grown by molecular-beam epitaxy. The oscillation of the reflectivity amplitude as a function of reflection angle is observed in the experiment. By doing a theoretical simulation, the concentration profile of Er atoms could be derived. It is shown that the originally grown delta-doped Er layer changes into an exponentially decayed function due to the Er segregation. The temperature dependence of the 1/e decay length indicates that the segregation is a kinetically limited process. The activation energy is determined to be 0.044 +/- 0.005 eV. [S0163-1829(99)11515-7].

In wireless local area networks (WLANs), link-layer multicast is a promising technology for many multimedia applications, e.g., video conference, as multicast frames can reach multiple clients simultaneously. However, the efficiency of multicast in WLANs is unsatisfactory since multicast frames are transmitted at low data rates to reach clients with poor channel quality. Moreover, the reliability of multicast cannot be guaranteed either, as multicast transmissions are not acknowledged. Some recent works have utilized smart antennas to improve multicast performance. But most of them require customized hardware and are not designed for the latest IEEE 802.11 standard, 802.11n WLANs. In this paper, we consider link-layer multicast in 802.11n WLANs with smart antennas. We partition clients into several groups, then select an antenna pattern from smart antennas and a multicast rate for each group, and transmit the same frame to each group. We first examine the gain of smart antennas and reliability of various 802.11n data rates for multicast in indoor WLANs via experiments. We then present the system model for multicast over smart antennas and formulate the problem into a mixed integer program. After that, we propose an optimal algorithm for the mixed integer program, under the condition that the packet reception ratio (PRR) of all antenna patterns and data rates is known for every client. As clients join and leave the network frequently and the wireless channel is time varying, we also propose an on-line algorithm that is able to adapt the partition of clients, antenna pattern and multicast rate for each group dynamically, based on PRR reports from clients. We have implemented the on-line algorithm on off-the-shelf WLAN products and conducted extensive experiments to evaluate the performance. The results show that the proposed algorithm can significantly improve multicast throughput compared to other strategies, and at the same time guarantee high PRR for all clients.

Recently, cooperative retransmissions have exhibited great potentials in enhancing the reliability and efficiency of wireless communications by exploring spatial diversity. With cooperative retransmissions, a cooperative node helps retransmit an overheard frame if the frame from a sender fails to reach the destination. Several cooperative retransmission schemes have been proposed for wireless local area networks (WLANs) in the literature. However, most of them require explicit coordination between the sender and the cooperative node before each retransmission, which results in a non-negligible overhead. Moreover, these schemes are not designed for the latest IEEE 802.11n standard, and are incompatible with the frame aggregation and block ACK mechanisms of 802.11n. In this paper, we propose an efficient cooperative retransmission MAC (CAR-MAC) protocol that utilizes new features of 802.11n and is compatible with standard 802.11n transmissions. In CAR-MAC, all nodes periodically broadcast a C-Beacon message to release their retransmitting capability, and each node selects a cooperative node based on received CBeacon messages. If some sub-frames in the aggregated frame from the sender fail to reach the destination, the cooperative node retransmits the failed sub-frames together with its own new sub frames, such that overhead from cooperative retransmissions is amortized by normal frame transmissions. We have theoretically analyzed the improvement on network throughput brought by CAR-MAC protocol. In addition, we have conducted extensive simulations to evaluate CAR-MAC protocol under various channel conditions. Both theoretical and simulation results show that the proposed protocol can greatly improve network throughput and reduce packet delay, compared with the 802.11n standard and existing cooperative retransmission schemes.

A wireless mesh network (WMN) is a special type of wireless ad-hoc network, which consists of mesh clients, mesh routers and gateways to the Internet, organized in a mesh topology. The mesh clients are often laptops, cell phones and other wireless devices. Mesh routers forward traffic between mesh clients and gateways. Despite a number of promising features provided by WMNs, such as low deployment cost, self-healing, etc., the throughput of WMNs is often limited by severe congestion and collisions, and thus cannot satisfy the increasing traffic demands of numerous applications. In this paper, we study how to maximize the throughput of IEEE 802.11n WMNs by joint routing and frame aggregation. Frame aggregation is to aggregate multiple frames into a large frame before transmission, to reduce communication overhead and alleviate collisions. We first show that previous frame aggregation strategies cannot achieve optimal network throughput. We then formulate the joint problem into a linear programming (LP) problem by considering traffic in the network as flow. As most previous algorithms for LP are centralized and difficult to deploy in large-scale WMNs, we propose a distributed algorithm to solve the formulated problem, in which each mesh router determines the amount of traffic flow for its adjacent links based on the traffic information of neighbors and interfering links. However, in realistic 802.11n WMNs, traffic is transmitted in frames instead of flow, and the traffic to different routers needs to be distinguished. Thus, we further provide an algorithm to determine the routing and frame aggregation strategy for each mesh router, using the traffic flow derived from the first algorithm. We have conducted extensive simulations to evaluate the proposed algorithms and the results demonstrate that the network throughput can be significantly improved compared with existing schemes.

As the latest IEEE 802.11 standard, 802.11n allows a maximum physical data rate as high as 600Mbps, making it a desirable candidate for wireless local area network (WLAN) deployment. In WLANs, access points (APs) are often densely deployed, and thus neighboring APs should be assigned with orthogonal channels to avoid performance degradation caused by interference. It is challenging to find the optimal channel assignment strategy, as the number of channels is very limited. Many channel assignment schemes have been proposed for WLANs in the literature. However, most of them were not designed for 802.11n WLANs, and did not consider the challenges from the new channel bonding and frame aggregation mechanisms. Moreover, the impact of multi-rate clients on channel assignment is not fully investigated yet. In this paper, we study channel assignment in multi-rate 802.11n WLANs, aiming at maximizing the network throughput. We first present a network model and an interference model, and estimate the client throughput based on them. We then formulate the channel assignment problem into a throughput optimization problem. As the formulated problem is NP-hard, we propose a distributed channel assignment algorithm to provide practical solutions. We have conducted extensive simulations to evaluate the proposed algorithm and the results show that the network throughput can be significantly improved compared with existing schemes.

A thin SiGe buffer layer grown on a Ge-island-decorated Si(100) surface has been prepared and used as the substrate for growing the ${\mathrm{Si}}_{6}$${\mathrm{Ge}}_{4}$ short-period superlattice with symmetrically distributed built-in strains. The Si/Ge superlattice is found to be free of threading dislocations, which is in favor of suppressing the intermixing of Ge and Si atoms at the superlattice interfaces. The Raman spectrum shows a very weak Si-Ge vibration mode, narrow peak widths of the Ge-Ge and Si-Si modes, and the disappearance of the Si optical-phonon mode from the substrate, which are indicative of the great improvement of the interfacial quality. \textcopyright{} 1996 The American Physical Society.

Photoabsorption and photoresponse of Si Si 1−x Ge x quantum wells are studied by using 45° unpolarized light field. Besides the free carrier absorption, the absorption peaks corresponding to both intersubband and intervalence band transitions are observed. We find that the intervalance band transitions are Ge composition dependent, but the intersubband transitions are not sensitive to Ge composition.

As the latest amendment of IEEE 802.11 standard, 802.11n allows a maximum raw data rate as high as 300Mbps, making it a desirable candidate for wireless local area network (WLAN) deployment. In typical deployment, the coverage areas of nearby access points (APs) usually overlap with one another to provide satisfactory coverage and seamless mobility support. Clients tend to associate (connect) to the AP with the strongest signal strength, which might lead to poor client throughput and overloaded APs. Although a number of AP association schemes have been proposed for IEEE 802.11 WLANs in previous studies, none of them have considered the frame aggregation feature in 802.11n. Moreover, the impact of legacy 802.11a/b/g clients in 802.11n WLANS has not been considered in AP association. To fill in this gap, in this paper we explore AP association for 802.11n with heterogeneous clients (802.11a/b/g/n). We first formulate it into an optimization problem based on a bi-dimensional Markov model, aiming at providing clients with the bandwidth proportional to their highest physical data rates, and then propose two heuristic AP association algorithms that can efficiently make online decisions on AP association. We have also conducted extensive simulations and experiments to validate the proposed algorithms. Our simulation results show that under hotspot client distribution, the proposed algorithms can boost the throughput of 802.11n clients and overall throughput by 106% and 89%, respectively, compared to other AP association schemes. Experiments also confirm the effectiveness of the algorithms in enhancing aggregated throughput, maintaining proportional fairness among clients and balancing load among APs.

The ion beam channeling technique has been used to characterize the SiGe/Si structure. It reveals different relative yield between and aligned spectra for strained SiGe layer, silicon buffer layer and silicon substrate which depends on different atomic arrangement.

In wireless local area networks (WLANs), collision-free channel access is desirable for real-time services that require guaranteed bandwidth and bounded delay. In WLANs with a single access point (AP), collision-free access can be achieved by applying the point coordination function (PCF), where the AP polls all associated clients for data transmissions. However, in larger WLANs with multiple APs, if there is no inter-AP coordination mechanism, concurrent transmissions from nearby basic service sets (BSSs) may collide and thus degrade service performance even if all APs operate on the PCF mode. So far only few schemes have been proposed to resolve this problem, and the client throughput in these schemes is quite limited due to the inaccurate modeling of polling conflicts. In this paper, we study client polling in multi-AP WLANs, with the objective of providing high-throughput, collision-free channel access for each client, and maximizing network capacity. We first give a WLAN framework in which the PCF of all APs is coordinated and clients are polled in a time slotted manner.We then formulate client polling into a time slot allocation problem and propose a collision-free polling scheme consisting of three procedures: (1) a basic polling procedure that determines the minimum number of time slots required to poll every client once to obtain the polling frequencies of all clients; (2) a complementary polling procedure that makes extra polls for APs that have idle time slots without causing collisions, to improve spatial reuse of the network; (3) a backup poll selecting procedure that finds backup clients to poll in case the current polled client has no data to transmit, to utilize the otherwise wasted bandwidth. We have conducted extensive simulations and compared it with two existing schemes. The simulation results show that the proposed scheme can provide high throughput and uniform channel access time for all clients, while boosting spatial reuse 2 to 3 times compared to other schemes.

Recent studies have shown that significant benefit can be achieved in wireless sensor networks (WSNs) by employing mobile collectors for data gathering via short-range communications. A typical scenario for such a scheme is that a mobile collector roams over the sensing field and pauses at some anchor points on its moving tour such that it can traverse the transmission range of all the sensors in the field and directly collect data from each sensor. In this paper, we study the performance optimization of such mobile data gathering by formulating it into a cost minimization problem constrained by the channel capacity, the minimum amount of data gathered from each sensor and the bound of total sojourn time at all anchor points. We assume that the cost of a sensor for a particular anchor point is a function of the data amount a sensor uploads to the mobile collector during its sojourn time at this anchor point. In order to provide an efficient and distributed algorithm, we decompose this global optimization problem into two subproblems to be solved by each sensor and the mobile collector, respectively. We show that such decomposition can be characterized as a pricing mechanism, in which each sensor independently adjusts its payment for the data uploading opportunity to the mobile collector based on the shadow prices of different anchor points. Correspondingly, we give an efficient algorithm to jointly solve the two subproblems. Our theoretical analysis demonstrates that the proposed algorithm can achieve the optimal data control for each sensor and the optimal sojourn time allocation for the mobile collector, which minimizes the overall network cost. Finally, extensive simulation results further validate that our algorithm achieves lower cost than the compared data gathering strategy.

Recently, several multi-channel MAC protocols have been proposed for wireless sensor networks (WSNs) to improve network capacity and boost energy efficiency. In addition, cooperative multiple-input multiple-output (MIMO) technique has been shown to be able to significantly enhance the energy efficiency of WSNs if properly configured. However, these two promising techniques have not been jointly utilized in WSNs. In this paper, we explore such a joint design by proposing a novel MAC protocol for WSNs that takes advantage of both multiple channels and cooperative MIMO. Specifically, sensor nodes in a WSN are organized into clusters and each cluster head selects some cooperative nodes to help forward traffic to or receive from other clusters by utilizing cooperative MIMO technique. For intra-cluster communications, different channels are assigned to adjacent clusters to reduce collisions, while for inter-cluster communications, cooperative MIMO links are scheduled to improve energy efficiency and concurrent transmissions are enabled by assigning different channels to them. We carry out extensive simulations and the results demonstrate that the proposed protocol can significantly increase throughput and improve energy efficiency compared to other schemes. For example, for a WSN with 150 nodes in a 250m × 250m field, with five or more available channels, the protocol can achieve over three times saturated throughput while saving up to 17% energy per bit for inter-cluster communications.

HV LDMOS on SOI has found wide applications such as lighting electronics and motor control due to its advantages over conventional LDMOS on bulk silicon. However, the design of optimized junctions with high breakdown voltages is commonly recognized to be difficult. This is partly because of the lack of analytical knowledge for the junctions design. In this study, various junctions were simulated by TCAD and analyzed from semiconductor physics point of view. It includes not only the junctions showing high breakdown voltages (>600V) but also the junctions showing relatively low breakdown voltages. The electrical field distribution, electrostatic potential distribution, depletion region and mobile carriers etc. were compared and analyzed to explain the reasons why a high breakdown voltage can be achieved for some junctions. Additionally, the breakdown voltage dependence on drift region doping profile was also studied.

In recent years, wireless mesh networks (WMNs) have been widely deployed to provide wireless access to the Internet. However, due to inter-link interference, the aggregated capacity of WMNs is limited, even with multiple channels. As a result, many links in WMNs are suppressed since interfering links cannot be active (i.e., transmitting packets) simultaneously. In this paper, we propose a joint design of channel assignment and space-division multiple access (SDMA) technique with the objective of maximizing the number of active links in WMNs. We assign different channels to transmission links based on their interference relationship to alleviate the interference. We also apply the SDMA technique to link scheduling, which enables two interfering links that share the same destination to communicate simultaneously on the same channel. By utilizing SDMA, more concurrent transmission links can be accommodated such that the network capacity can be greatly improved. We formulate this joint design into an optimization problem, prove its NP-hardness and then provide two heuristic algorithms to give practically good solutions to the problem. %David update begin Our simulation results demonstrate that when 90% SDMA pairs are compatible, the proposed algorithms can increase the percentage of active links in a WMN by up to 40% as compared to non-SDMA schedules.

With more important function in information society, software dependability has been in higher demand. Web application vulnerability has become one of the biggest threats for software security. Detecting and solving vulnerability is the effective way to enhance software dependability. Most active method traverses all web links and interactive units in traversing step, which is easy to cause low efficiency and no pertinence. This paper focuses on characteristic of web application, especially web pages and presents one traversing model based on high-related rule, which make detection more efficient. From hacker’s view, this model applies the HITS algorithm to generating a series of pages which may be used by hackers as attacking. Due to ignoring content in web pages for HITS algorithm, we adapt improved Apriori algorithm to get optimized frequency set, on basis of which we deduce high-related rule between properties of interactive unit and way of attacking. Finally, this paper presents the traversing model for web application vulnerability detection

Currently, the most widely used treatment for diabetes is the daily subcutaneous injection of recombinant human insulin. Daily injections, however, cannot match the physiological biphasic behavior of normal insulin release, nor can they precisely meet the demands of food intake, exercise, and stress. Cellular encapsulation, or immunoisolation, is a possible solution to this problem. This cell-based therapy allows patients to receive the benefits of more physiological insulin and blood glucose regulation, without the need for immunosuppressants that are associated with organ or cell transplantation.Immunoisolation capsules were fabricated out of aluminum and aluminum oxide using a two-step anodization procedure. The diffusion behavior of glucose, immunoglobulin G (IgG), and insulin were measured. Furthermore, the functionality and viability of encapsulated MIN6 cells were tested. Finally, live cells were stained and imaged using confocal microscopy.Data indicated that this device is effective in allowing the transport of relevant molecules such as glucose and insulin, while at the same time significantly impeding the transport of IgG, suggesting that it would be efficacious in protecting cell grafts in vivo. Furthermore, encapsulated cells were able to respond dynamically to glucose input signals. Finally, cell staining showed that the viability of encapsulated cells is maintained after 24 h, although the cells appear to be more heavily concentrated at the area that is closest to the membrane.This study has shown that nanoporous alumina membranes, with well-controlled pore sizes, can be used for the encapsulation of therapeutic cells and may provide an alternative encapsulation strategy for the treatment of diabetes.

Two wireless, passive remote query magnetism-based glucose sensors, which operate in combination with a mass and volume changing glucose responsive polymer, are presented. One sensor design is based upon the magnetostatic coupling of magnetically soft thin-film elements, as the polymer volume changes in response to glucose concentration so does the magnetostatic coupling between elements. In response to a time varying magnetic field, upon reversal of the magnetization vector of the elements the magnetostatic coupling determines the time rate of change of magnetic flux, and hence the amplitude of the voltage spike generated in a pick-up coil. The other sensor consists of a free-standing magnetoelastic thick-film, coated with a thin layer of the glucose responsive polymer. In response to a time varying magnetic field the sensor mechanically vibrates at a characteristic resonant frequency, the characteristic resonant frequency of the sensor linearly tracks the change in mass of the glucose responsive polymer.

Grazing incidence x-ray diffraction measurements at different grazing angles for self-organized Ge dots grown on Si(001) are carried out by using synchrotron radiation as a light source. Deformation strains in the substrate underneath or surrounding the dots induced by formation of Ge quantum dots are investigated. Besides a tensile strain existing underneath the dots, a peak located at the higher angle side of Si(220) or Si(400) is observed for the first time, the origin of this peak is attributed to the near surface compressive strain in the peripheral substrate regions surrounding the Ge dots. This compressive strain corresponds to a -0.8% lattice constant change parallel to the interface.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We reported deep-level-free band edge luminescence from strained SiGe/Si multiple quantum well structures grown by conventional solid source Si MBE. No-phonon (NP) transitions due to symmetry-breaking alloy disordering in SiGe layers and transverse optical (TO) phonon replicas were clearly identified. A high quality of crystallinity is essential to the efficient luminescence. The choice of a higher growth temperature, Ts equals 870 degree(s)C, beyond the conventional growth temperature window 400-600 degree(s)C, was found to be important for radioactive recombination in SiGe/Si QWs structures.

An oxygen δ-doped Si multilayer structure has been grown by molecular beam epitaxy (MBE). Thermal oxidation of a Si layer prepared by an MBE system at a low oxygen partial pressure resulted in a thin ordered oxide layer with a very flat surface. On the ordered oxide, Si was epitaxied through the solid phase epitaxy. Five periods of Si(2 nm)/SiO x (1 nm) multilayers were grown successfully. The O-doped Si layer (SiO x ) was composed of 7 atomic layers and the crystalline structure of the SiO x layer was the same as that of the Si substrate but had a relatively transverse displacement. The in-plane stress restricted the number of the oxide layers grown to a thickness of less than 6 atomic layers. This structure may be the gateway for realizing Si-based quantum wells.

Interfacial defects related to the residual carbon on the hydrogenterminated Si(100) surface have been studied using the deep-level transient spectroscopy (DLTS) technique. The defect level is found to be donorlike which compensates the acceptor impurity at the interface. With a fast load-in and a two-step annealing, the defect density can be suppressed below the DLTS detection limit of 1012 cm-3.

Effects of perfusion flow rate and three vasoconstrictors, phenylephrine, prostaglandin F2 alpha (PGF2 alpha) and serotonin, on isolated, perfused brain preparations of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY) were investigated. The basal perfusion pressure of the cerebral vascular beds at a flow rate of 2.5 ml/min was 48 +/- 3 mm Hg (n = 11) in SHR and 32 +/- 2 mm Hg (n = 12) in WKY (P less than 0.005). The perfusion pressures at all flow rates tested (2.5-6.5 ml/min) in SHR were significantly greater than those in WKY. Concentration-perfusion pressure curves for the vasoconstrictors showed that the brain vascular bed was much more reactive to serotonin compared with phenylephrine and PGF2 alpha. EC50 values (-logM) for serotonin in the perfused brains of SHR and WKY were 7.0 +/- 0.06 (n = 10) and 6.5 +/- 0.06 (n = 11), respectively (P less than 0.01). There were no differences in EC50 values for phenylephrine or PGF2 alpha between SHR and WKY. Exogenous serotonin and phenylephrine caused significantly greater maximal vasoconstrictor responses in SHR compared with WKY, while the pressor response to PGF2 alpha was very weak and no significant difference between SHR and WKY preparations was observed. These results indicate that cerebral vascular beds in SHR exhibit higher cerebrovascular resistance than those in WKY. and that reactivity and sensitivity to serotonin and reactivity to phenylephrine in SHR rats are enhanced to a greater extent compared to WKY.