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Maintaining tissue homeostasis requires proper regulation of stem cell differentiation. The Waddington landscape suggests that gene circuits in a cell form a potential landscape of different cell types, with cells developing into different cell types following attractors of the probability landscape. However, it remains unclear how adult stem cells balance the trade-off between self-renewal and differentiation. We propose that random inheritance of epigenetic states plays a crucial role in stem cell differentiation and develop a hybrid model of stem cell differentiation induced by epigenetic modifications. Our model integrates a gene regulation network, epigenetic state inheritance, and cell regeneration to form multi-scale dynamics ranging from transcription regulation to cell population. Our simulation investigates how random inheritance of epigenetic states during cell division can automatically induce cell differentiation, dedifferentiation, and transdifferentiation. We show that interfering with epigenetic modifications or introducing extra transcription factors can regulate the probabilities of dedifferentiation and transdifferentiation, revealing the mechanism of cell reprogramming. Thisin silicomodel offers insights into the mechanism of stem cell differentiation and cell reprogramming.

Malignant peripheral nerve sheath tumor (MPNST), a highly malignant tumor that arises in peripheral nerve tissues, is known to be highly resistant to radiation and chemotherapy. Although there are several reports on genetic mutations and epigenetic changes that define the pathogenesis of MPNST, there is insufficient information regarding the microenvironment that contributes to the malignancy of MPNST. In the present study, we demonstrate that adrenaline increases the cancer stem cell population in MPNST. This effect is mediated by adrenaline stimulation of beta-2 adrenergic receptor (ADRB2), which activates the Hippo transducer, YAP/TAZ. Inhibition and RNAi experiments revealed that inhibition of ADRB2 attenuated the adrenaline-triggered activity of YAP/TAZ and subsequently attenuated MPNST cells stemness. Furthermore, ADRB2-YAP/TAZ axis was confirmed in the MPNST patients' specimens. The prognosis of patients with high levels of ADRB2 was found to be significantly worse. These data show that adrenaline exacerbates MPNST prognosis and may aid the development of new treatment strategies for MPNST.

Tourism destinations are now facing a dilemma choice of controlling the epidemic or developing the economy. This paper takes Macao, a typical international tourist city, as an example to study the strategy of tourist source control during the COVID-19 period. According to the published epidemic data of Macao, this study has established an improved SEIR (Susceptible-Exposed-Infected-Recovered) model, formulated six control strategies against the current epidemic, and used the model above to simulate the time required for all confirmed cases to recover and discharge under different strategies. By taking into consideration the gross revenue of Macao’s gambling industry from 2017 to 2019, the impact of different strategies on the economy is predicted and three control strategies are found to be feasible. This study shows that an effective way to break through the above dilemma is to design the tourist management strategy by screening the source of passengers and controlling the upper limit of capacity of destination. These findings provide a scientific basis for tourism destinations in formulating public policies. The improved SEIR model is more consistent with the actual conversion rule of patients in the current COVID-19 epidemic, and it can be applied to further public health related research.

Cell plasticity is important for tissue developments during which somatic cells may switch between distinct states. Genetic networks to yield multistability are usually required to yield multiple states, and either external stimuli or noise in gene expressions are trigger signals to induce cell-type switches. In many biological systems, cells show highly plasticity and can switch between different states spontaneously, but maintaining the dynamic equilibrium of the cell population. Here, we considered a mechanism of spontaneous cell-type switches through the combination between gene regulation network and stochastic epigenetic state transitions. We presented a mathematical model that consists of a standard positive feedback loop with changes of histone modifications during cell cycling. Based on the model, nucleosome state of an associated gene is a random process during cell cycling, and hence introduces an inherent noise to gene expression, which can automatically induce cell-type switches in cell cycling. Our model reveals a simple mechanism of spontaneous cell-type switches through a stochastic histone modification inheritance during cell cycle. This mechanism is inherent to the normal cell cycle process, and is independent to the external signals.

Cell plasticity is important for tissue developments during which somatic cells may switch between distinct states. Genetic networks to yield multistable states are usually required to yield multiple states, and either external stimuli or noise in gene expressions are trigger signals to induce cell-type switches between the states. In many biological systems, cells show highly plasticity and can switch between different state spontaneously, but maintaining the dynamic equilibrium of the cell population. Here, we considered a mechanism of spontaneous cell-type switches through the combination between gene regulation network and stochastic epigenetic state transitions. We presented a mathematical model that consists of a standard positive feedback loop with changes of histone modifications during with cell cycling. Based on the model, nucleosome state of an associated gene is a random process during cell cycling, and hence introduces an inherent noise to gene expression, which can automatically induce cell-type switches in cell cycling. Our model reveals a simple mechanism of spontaneous cell-type switches through a stochastic histone modification inheritance during cell cycle. This mechanism is inherent to the normal cell cycle process, and is independent to the external signals.

Antibiotic administration, while facilitating clearance of targeted infections, also perturbs commensal microbial communities. Previous studies have all focused on the effects of short term use of antibiotics. Here, we focus on the effects of long term use of antibiotic on gut microbiota and immunity. BALB/c mice received saline or different doses of ceftriaxone sodium (100, 200 and 400 mg/mL) via daily gavage for 150 days. Alterations of fecal microbiota, small intestine histopathology, body weight, spleen index, serum IgG, mucus SIgA, IFN-γ/IL-4 ratio, CD4/CD8 ratio and CD4+CD25+ cells were evaluated. Long term ceftriaxone sodium administration resulted in gut microbiota dysbiosis, intestine histological lesions, growth inhibition, spleen index reducing. The immune defense ability reduced as serum IgG and mucus SIgA decreased significantly. Not only the immune defense, long term ceftriaxone administration also affected immune regulation. The IFN-γ/IL-4 and CD4/CD8 ratios increased, the CD4+CD25+ cells reduced on days 30 and 60 after ceftriaxone administration. However, after 90 days of ceftriaxone administration, the IFN-γ/IL-4, CD4/CD8 ratios and CD4+CD25+ cells restored, which indicated a new balance of immune regulation had been formed. Overall, these findings contribute to our understanding of long term antibiotic administration influencing gut microbiota and immunity.

As is known, a large-scale sea-floor observatory is comprised of hundreds of instruments. Integration of new instruments into such a large observatory is a very tedious, repetitive but tough task. Manual configuration is error-prone, so an automatic configuration mechanism is needed. MBARI PUCK is designed for this purpose. But it is not easy to make a hardware puck. So a virtual puck, called Cloud PUCK, is proposed in this paper. Cloud PUCK also makes some modify to achieve the high scalability and interoperability requirement of the sea-floor observatory.

Multihop cellular networks (MCNs) have drawn tremendous attention due to its high throughput and extensive coverage. However, there are still three issues not well addressed. With the existence of relay stations (RSs), how to efficiently allocate frequency resource to relay links becomes a challenging design issue. For mobile stations (MSs) near the cell edge, cochannel interference (CCI) become severe, which significantly affects the network performance. Furthermore, the unbalanced user distribution will result in traffic congestion and inability to guarantee quality of service (QoS). To address these problems, we propose a quantitative study on adaptive resource allocation schemes by jointly considering interference coordination (IC) and load balancing (LB) in MCNs. In this paper, we focus on the downlink of OFDMA-based MCNs with time division duplex (TDD) mode, and analyze the characteristics of resource allocation according to IEEE 802.16j/m specification. We also design a novel frequency reuse scheme to mitigate interference and maintain high spectral efficiency, and provide practical LB-based handover mechanisms which can evenly distribute the traffic and guarantee users' QoS. Our study shows that our scheme not only meets the requirement on coverage, but also improves the throughput while accommodating more users in MCNs.

In high mobility areas such as shopping malls and transportation stations, mobile users tend to move in and out in a bursty fashion, and hence location update (LU) and paging signaling cause substantial traffic burden to the cellular networks, leading to signaling congestion. This poses a great challenge to the system design for wireless cellular systems. Traditional cellular systems cannot cope with this situation very well. However, with the ad hoc operational mode recently introduced into the cellular systems, the added multi-hop relaying via mobile devices provides a new way to mitigate location management traffic. In this paper, based on this new architecture, we propose a novel scheme, called aggregative location management, which aggregates multiple location updates into group location updates. For the scenarios of high capacity transit (HCT) systems, we use this grouping scheme to alleviate the signaling traffic when mobile users in an HCT move into new location areas. For other scenarios with mass arrivals of LU requests, we develop a generic aggregative location management scheme in which LU requests can be first aggregated by designated mobile devices and then are periodically sent to the location registers. Performance evaluation is carried out and shows their significant effectiveness.

The identities and concentrations of low-molecular-weight organic acids (LMWOAs) were determined by ion chromatography throughout a 20-m water column in Hongfeng Lake, China. The spatiotemporal variations of LMWOAs and their contributions to dissolved organic matter (DOM) in a research period of 24 hr were also investigated. The results demonstrated that five LMWOAs (lactic, acetic, pyruvic, sorbic, oxalic acid) were detected, and their total concentration and proportion in DOC were 6.55 micromol/L and 7.47%. Their average levels were 2.50, 0.65, 2.35, 0.96 and 0.09 micromol/L, respectively. LMWOAs were higher during daytime (10:00-18:00 on Jun 13, 2008) than nighttime (21:00-6:00 the next morning), in particular 4.99 micromol/L high in the epilimnion (or = 1 m water depth), reflecting the fact that direct import from terrigenous sources and photochemical production from humic materials were dominant during LMWOAs' origin and accumulation. The same factors caused LMWOAs to be 0.63 micromol/L in the epilimnion higher than in the hypolimnion. The rapid decrease of total organic acid (TOA) up until 18:00 mainly resulted from bio-uptake and mineralization in the hypolimnion (1 m water depth). Pyruvic acid increased with time in the epilimnion and decreased in the hypolimnion, largely related to the two contrary processes of continuous degradation and synthesis of macromolecular organic matter during life materials' cycle mediated by organisms. Simultaneously, plankton behavior and thermal stratification played a pivotal role in LMWOAs' behavior in the water column, causing decreasing and increasing profiles. The distribution of LMWOAs represents an interesting resource for biogeochemical research of DOM in aquatic ecosystems.

Nowadays integrated network ensures the security of information transmission by adding encrypt, simple authentication and so on, but it lacks effective means to secure the verification, authorization, confidentiality and completeness of the information, especially in the wireless network, and as a result of the openness of the transmission medium, it is particularly important to guarantee its security. This paper focuses on the modern cryptosystem to establish and realize a safe and practical integrated network security strategy model. The architecture of the model consists of three portions, namely security system, secure connection of network and security transmission of data, key management.

Low-molecular-weight organic acids (LMWOAs) in eutrophic lake water of Dianchi, Southwestern China Plateau were investigated diurnally and vertically using ion chromatography. Two profiles (P1 and P2) were studied due to the difference of hydrochemical features. Lactic, formic, pyruvic and oxalic acid were detected as major components at P1 and P2 which were on average 7.98 and 6.53 micromol/L, respectively, corresponding to their proportions of 2.68% and 2.48% relative to DOC. Pyruvic acid was regarded as the uppermost species at P1 and P2, reaching up to 3.82 and 3.35 micromol/L and accounting for 47.9% and 51.3%, respectively, in individual TOA. Although humus were of biogenetic production at both sites, the significant negative correlation between diurnal variations of TOAs, fluorescence intensity (FI) of protein-like components and humic-like components at P1 indicated LMWOAs were greatly originated from bacterioplankton excretion and degradation. However, correlations between diurnal variations of humic-like FI and physicochemical parameters demonstrated algal origination of LMWOAs at P2. Although content of humus was high, TOA at P2 was 1.45 micromol/L lower than that at P1, due to the co-influence of more intense photo-oxidation and aggregation at P2. Therefore, TOAs exhibited quite opposite diurnal variation trends of increasing-decreasing and decreasing-increasing at P1 and P2, respectively. Except for impact of solar radiation, bacterial decomposition and assimilation rendered shifts of maximal LMWOAs along water column at P1. Covering with massive algae, UV rays penetrated shallower depth that LMWOAs assembled in surface layer water before 18:00 at P2 and represented decreasing profiles.

Handoff performance is a critical issue for mobile users in wireless cellular networks, such as GSM networks, 3G networks, and next generation networks (NGNs). When ad hoc mode is introduced to cellular networks, multi-hop handoffs become inevitable, which brings in new challenging issues to network designers, such as how to reduce the call dropping rate, how to simplify the multi-hop handoff processes, and how to take more advantage of ad hoc mode for better resource management, and most of these issues have not been well addressed as yet. In this paper, we will address some of the issues and propose a scheme, Ad-hoc-Network---Embedded handoff Assisting Scheme (ANHOA), which utilizes the self-organizing feature of ad hoc networks to facilitate handoffs in cellular networks and provide an auxiliary way for mobile users to handoff across different cells. Moreover, we also propose a scheme enabling each BS to find the feasible minimum reservation for handoff calls based on the knowledge of adjacent cells' traffic information. Due to the use of multi-hop connections, our scheme can apparently alleviate the reservation requirement and lower the call blocking rate while retaining higher spectrum efficiency. We further provide a framework for information exchange among adjacent cells, which can dynamically balance the load among cells. Through this study, we demonstrate how we can utilize ad hoc mode in cellular systems to significantly improve the handoff performance.

Experiments have shown that in embryonic stem cells, the promoters of many lineage-control genes contain “bivalent domains”, within which the nucleosomes possess both active (H3K4me3) and repressive (H3K27me3) marks. Such bivalent modifications play important roles in maintaining pluripotency in embryonic stem cells. Here, to investigate gene expression dynamics when there are regulations in bivalent histone modifications and random partition in cell divisions, we study how positive feedback to histone methylation/demethylation controls the transition dynamics of the histone modification patterns along with cell cycles. We constructed a computational model that includes dynamics of histone marks, three-stage chromatin state transitions, transcription and translation, feedbacks from protein product to enzymes to regulate the addition and removal of histone marks, and the inheritance of nucleosome state between cell cycles. The model reveals how dynamics of both nucleosome state transition and gene expression are dependent on the enzyme activities and feedback regulations. Results show that the combination of stochastic histone modification at each cell division and the deterministic feedback regulation work together to adjust the dynamics of chromatin state transition in stem cell regenerations.

The event-driven nature of wireless sensor networks (WSNs) leads to unpredictable network load. As a result, congestion may occur at sensors that receive more data than they can forward, which causes energy waste, throughput reduction, and packet loss. In this paper, we propose a rate-based fairness-aware congestion control (FACC) protocol, which controls congestion and achieves approximately fair bandwidth allocation for different flows. In FACC, we categorize intermediate relaying sensor nodes into near-source nodes and near-sink nodes. Near-source nodes maintain a per-flow state and allocate an approximately fair rate to each passing flow. On the other hand, near-sink nodes do not need to maintain a per-flow state and use a lightweight probabilistic dropping algorithm based on queue occupancy and hit frequency. Our simulation results and analysis show that FACC provides better performance than previous approaches in terms of throughput, packet loss, energy efficiency, and fairness.

In this paper, we study the impacts of physical carrier sensing and channel rate on the throughput of 802.11 wireless networks with chain topology. Firstly, we show that by adopting different carrier sensing thresholds for the RTS and CTS transmissions, the blocking problem caused by exposed terminals can be greatly alleviated. In 802.11 wireless networks with this modification, the spatial reuse ratio under certain channel rates can be increased to 13, which is the highest value to our best knowledge. Secondly, in multi-rate networks, we demonstrate that 13 is still the best value of spatial reuse ratio in terms of maximizing the achievable data rate under certain conditions. Thirdly, this paper proposes a new method to address the intra-flow contention by decreasing the carrier sensing threshold of the source node. This method requires less response time than that of the traditional method which adjusts the backoff window size. Finally, extensive simulations are implemented in NS2 and the results show that our scheme significantly improves the throughput of 802.11 wireless networks with chain topology.

Background and Purpose—Although experimental studies have suggested that tea consumption may reduce the risk of ischemic stroke, available epidemiological evidence is equivocal, mainly due to the lack of accurate measurements on tea exposure. This study aims to ascertain the relationship between tea drinking and ischemic stroke risk.Methods—A case-control study was conducted in southern China from 2007 to 2008. A total of 374 patients with incident ischemic stroke and 464 control subjects (mean age, 69 years) were recruited from 3 hospitals in Foshan. Information on frequency and duration of tea drinking, quantity of dried tea leaves, and types of tea consumed, together with habitual diet and lifestyle characteristics, was obtained from participants using a validated and reliable questionnaire. Logistic regression analyses were performed for tea consumption variables accounting for confounders that affect the ischemic stroke risk.Results—A significant decrease in ischemic stroke risk was observed for drinking at least one cup of tea weekly (P=0.015) when compared with infrequent or nondrinkers, the risk reduction being largest by drinking one to 2 cups of green or oolong tea daily. Significant inverse dose-response relationships were also found for years of drinking and the amount of dried tea leaves brewed. The adjusted ORs for the highest level of consumption in terms of frequency of intake, duration of drinking, and average tea leaves brewed were 0.61 (95% CI, 0.40 to 0.94), 0.40 (95% CI, 0.25 to 0.64), and 0.27 (95% CI, 0.16 to 0.46), respectively.Conclusion—Long-term tea consumption is associated with reduced risk of ischemic stroke.

Summary The composition and contents of low molecular weight organic acids (LMWOAs) were determined, their contributions to dissolved organic carbon (DOC) and vertical profiles were investigated in sediment porewaters of six lakes, China: Lake Sihai-Longwan (SHLW), Lake Bosten (BST), Lake Qinghai (QH), Lake Chenghai (CH), Lake Erhai (EH) and Lake Dianchi (DC). The sources and behaviors of LMWOAs during early diagenesis were also discussed. The results show that up to eight species of LMWOAs were detected in those sediment porewaters: lactic acid, acetic acid, formic acid, methanesulfonic acid (MSA), pyruvic acid, trifluoroacetic acid (TFA), sorbic acid and oxalic acid; acetic acid was the predominant species. The contents of organic acids in six lakes decrease in the rank order of QH > SHLW > BST > EH > DC > CH, with the total amount of organic acids in the northern lakes being about 27 times higher than those in the southern lakes. In total amounts of various organic acids, acetic acid were the highest and MSA was the lowest, they were 62.7 and 0.3 μM, respectively. The highest total amount of organic acids was in QH, with the average value of 92.0 μM and the contribution to DOC was 10.9% followed by SHLW, BST, EH and DC, which were 43.7 μM, 2.7%; 42.3 μM, 5.6%; 5.6 μM, 1.1%; 4.4 μM, 0.7%, respectively. Organic acid was the lowest in CH, with the average value of 0.5 μM and the contribution to DOC was just 0.04%. The main organic acids were acetic acid, pyruvic acid, sorbic acid and formic acid in SHLW, BST, DC and CH, lactic acid in both EH and QH. Vertical profiles of LMWOAs varied among different species and lakes due to the sources and complex microbial processes in early diagenesis. This study suggests LMWOAs played a significant role in the sources and transformation of DOM in the sediments in lakes.

The enhanced distributed channel access (EDCA) of IEEE 802.11e has been standardized to support quality of service (QoS) in wireless local area networks (LANs). The EDCA statistically supports the QoS by differentiating the probability of channel access among different priority traffic and does not provide the deterministically prioritized channel access for high-priority traffic, such as voice or real-time video. Therefore, lower priority traffic still affects the performance of higher priority traffic. In this paper, we propose a simple and effective scheme called deterministic priority channel access (DPCA) to improve the QoS performance of the EDCA mechanism. To provide guaranteed channel access to multimedia applications, the proposed scheme uses a busy tone to limit the transmissions of lower priority traffic when higher priority traffic has packets to send. Performance evaluation is conducted using both numerical analysis and simulation and shows that the proposed scheme significantly outperforms the EDCA in terms of throughput, delay, delay jitter, and packet drop ratio under a wide range of contention level.

Using multi-channel MAC protocols in mobile ad hoc networks (MANETs) is a promising way to improve the through-put performance. Channel assignment, which directly determines the efficiency of the frequency utilization, is the critical part of multi-channel schemes. Current 802.11-like schemes of multi-channel MAC do not efficiently use the multiple channels due to the overhead caused by channel assignment. Moreover, the control channel saturation problem limits the number of channels of these previous schemes. In this paper, we propose a new scheme called SAM-MAC (Self-Adjustable Multi-channel MAC), which features with one common channel and two half-duplex transceivers for each node. A method called self-adjustment is used to reassign the channels and balance the traffic on different channels. Due to less contention in common channel and smaller channel assignment overhead, this scheme increases the throughput compared with previous approaches. Control channels are free from saturation problem and can furthermore be used for data transmission.

Ischemic stroke is one of the leading causes of mortality and morbidity in the world. A large number of studies have observed the beneficial effects of soy protein and soy polyunsaturated fat in lowering blood cholesterol, reducing blood pressure and improving cardiovascular health. This study aims to investigate the potential of a soy food diet in the prevention of ischemic stroke through evaluation of evidence from clinical trials, meta-analyses, experimental and epidemiological studies.

TDMA-based MAC schemes suit WBANs due to such networks' simple star topology and power limitations. In conventional ad hoc wireless networks, the specific arrangement of reservations within a TDMA frame is of minor importance as long as all nodes asking for a reservation are granted one within a frame interval. Yet emergency event preemptions or possible sensor-initiated and uncoordinated extensions of granted schedules, which seem inevitable for WBAN applications, make reservation arrangement an important problem. Here, such events could transgress an already scheduled reservation of maybe another node, jeopardizing the latter's transmission opportunity. This is more of an issue if we consider the power-limited nature of WBAN nodes, limiting the time they can keep awake looking forward for a maybe delayed transmission opportunity. In this paper we study the optimal arrangement of slave nodes' reservations which seeks to best fulfill the traffics' QoS requirements subject to a power consumption constraint. In that we account for nodes' reservation lengths, traffic QoS requirements, and the corresponding statistical characteristics of reservation extensions and emergencies. Our strategy protects the reservations of the more QoS-constrained of slaves' applications against the possible preemptions of others and also provides them with adequate bandwidth if they ever needed to extend their reservation on the fly.

By incorporating relay technologies into cellular systems, multi-hop relay networks (MRNs) can provide higher throughput and wider coverage, but it is impossible to guarantee quality of service (QoS) requirements for users at the cell edge and in hot spots due to severe co-channel interference (CCI) and load imbalance. This paper proposes an adaptive resource allocation scheme with a joint consideration of interference coordination (IC) & load balancing (LB), and analyzes the downlink of orthogonal frequency division multiple access (OFDMA) based MRNs with time division duplex (TDD) mode. We present a novel frequency reuse scheme for MRNs to mitigate CCI and maintain high spectral efficiency. We also provide practical LB-based handover mechanisms to evenly distribute users and guarantee the users' QoS. Extensive simulations demonstrate that our scheme not only satisfies the requirement of coverage probability, but also improves the throughput and accommodates more users in MRNs.

The multi-hop cellular network (MCN) is an evolved paradigm for mobile communications, which integrates the ad hoc characteristics into the conventional cellular systems. Similar to ad hoc networks, the performance of MCNs relies on the hypothesis that each node accepts to forward traffic for the benefit of others, which may not hold with the possible presence of selfish users. In order to stimulate the collaboration among mobile nodes in MCNs, in this paper, we propose a light-weighted secure incentive protocol (LIP). We introduce a novel reward model, in which not the source and/or the destination but the network operator credits the forwarding nodes. It is shown that our model is much more realistic for MCNs in practice and simplifies the payment scheme design as well. LIP exploits a reactive receipt-submission mechanism to identify node behavior, which significantly reduces the communication overhead. Security analysis shows that LIP can resist various attacks. The efficiency of LIP is validated through the performance evaluation.

With the development of SNS(social network service), social network has become more and more important. The problem of how to discover users' (including the Internet and the telecommunication network) social network from users' interaction detail between each other starts to be the focus problem of researchers. Basing on the analysis of telecommunication call data, this paper studied how CDRs(Call Detail Records) can be transformed to call graph. And then the concept of TF(Telecommunication Family) and a clustering algorithm to discover TFs is proposed, which bases on call graph. Our empirical study shows that the proposed algorithm is promising in discovering TFs from CDRs.

When many cellular users take high capacity transit (HCT), a group of mobile terminals (MTs) may have to initiate handoffs and location updates more or less at the same time, which will cause congestion on the random access control channel (RACH), leading to many handoff and location update failures. To overcome this problem, we propose a new scheme, called GHA/RALU (Group Handoff Avoidance/Rate Adjusted Location Update Scheme), to deal with this group mobility issue. The idea is first to delay the normal location update (NLU) requests until the group handoff requests are completed and then spread the NLU requests within a calculated time interval based on the available bandwidth of the RACH. Our analysis shows that the proposed scheme significantly improves the success probability of the group handoffs and NLUs, saves the RACH resource, and accelerates the handoff initiated by the moving-in-together MTs.

Wireless Relay networks have become very important technologies in the future wireless systems. Current research works mostly focus on scenarios where relay stations are either stationary or mobile with uniform velocity. However, in many applications, relay stations are mobile with irregular patterns. In particular, when mobile relay stations (MRSs) are deployed to complement the cellular systems, many issues such as handoff should be carefully investigated. In this paper, we focus on the handoff problem and propose a new handoff decision algorithm based on the relative velocities of user equipment (UE) to the serving access point (AP) and the target AP. We have show that the proposed handoff algorithm can significantly improve the handoff successful rate when the mobile relay station changes its moving patterns.

As all-IP feature becomes dominant in the next generation networks (NGNs), ad hoc mode is gaining more attention as an appealing addition to cellular networks. Consequently, multi-hop handoffs become inevitable, which bring challenging issues to network designers. Handoff dropping (HOD) rate and the bandwidth reservation for the required HOD rate are two important metrics to evaluate the handoff performance of a cellular system. By introducing ad hoc mode into cellular systems, we can either achieve lower HOD rate or reserve less bandwidth for the same required HOD rate. In this paper, we incorporate traffic information from neighboring BSs and propose an algorithm to find the minimum bandwidth reservation for each BS. Since its performance greatly depends on the access probability to the adjacent cells, we further propose to utilize the embedded ad hoc networks to gather the traffic load information of neighboring cells. With such information, handoff calls can effectively select the best paths to the proper BSs. It has been demonstrated that our scheme can significantly improve the system performance.

The composition and vertical profiles of low molecular-weight organic acids (LMWOAs) and the contribution of them to dissolved organic matter (DOM) in sediment porewaters in Bosten Lake, Xinjiang, China were investigated. The results showed that total concentration of LMWOAs was up to 94.5 micromol/L and their proportion in DOM was 5.6%, suggesting that LMWOAs were important chemical components in DOM in lake sediment porewaters. Among the seven LMWOAs, pyruvic and acetic acid had the highest concentrations with 26.30 and 8.31 micromol/L, accounting for 51.4% and 14.92% of LMWOAs, respectively. Trifluoroacetic and sorbic acid had the lowest concentrations, indicating that the compositions of LMWOAs in relative reducing environments were largely different from those reported in glacier, atmosphere and soils. The concentrations of lactic, acetic, formic, sorbic and oxalic acid decreased with increasing depth, probably relating to stronger microbial activities in the initial stage of early diagenesis. Trifluoroacetic acid was mainly anthropogenic with its concentration, showing a diffusive trend from the surface to bottom sediments. The concentrations of lactic acid and nitrate generally showed a consistent profile. The increasing concentration of pyruvic acid in the vertical profile was just opposite to that of sulfate, revealing a significant negative relationship between them. Oxalic acid remained constant except for an obvious peak at 6 cm depth. The results indicated the diversities in sources and behaviors for various LMWOAs during early diagenesis in sediments.

The current low throughput of wireless ad hoc networks is greatly caused by the inefficiency of spectrum usage. With distributed scheduling/spectrum allocation, better spectrum efficiency can be achieved. However, most distributed algorithms consider the neighbors' traffic independent of each other and ignore the multi-hop nature of flows, leading to the spectrum wastage and inefficiency. By incorporating the multihop nature of flows, we propose a new distributed scheme based on IEEE 802.11 standard, namely “2-hop MAC”. Nodes collect traffic dependency information as well as traffic demand information from neighbors and allocate spectrum distributedly with the knowledge of more accurate traffic demand of the nodes in the neighborhood. Extensive simulation study shows that our proposed scheme can significantly improve the network performance and spectrum efficiency.