Access Scheduling Research Articles

Baclofen, raclopride, and naltrexone differentially reduce solid fat emulsion intake under limited access conditions

Previous work in rats has demonstrated that an Intermittent (Monday, Wednesday, Friday) schedule of access promotes binge-type consumption of 100% vegetable shortening during a 1-h period of availability. The present study used novel shortening-derived stable solid emulsions of various fat concentrations. These emulsions were the consistency of pudding and did not demonstrate oil and water phase separation previously reported with oil-based liquid emulsions. Male Sprague–Dawley rats were grouped according to schedule of access (Daily or Intermittent) to one of three concentrations (18%, 32%, 56%) of solid fat emulsion. There were no significant Intermittent vs. Daily differences in amount consumed, due to high intakes in all groups. This indicated the acceptability of the emulsions. Baclofen (GABA B agonist) and raclopride (D2-like antagonist) both significantly reduced emulsion intake in all Daily groups, but only in the 56% fat Intermittent group. Naltrexone (opioid antagonist), in contrast, significantly reduced 32% and 56% fat emulsion intake in the Intermittent, as well as the Daily groups. These results indicate that the fat intake-reducing effects of GABA B activation and D 2 blockade depend upon fat concentration and schedule of fat access, while the fat intake-reducing effects of opioid blockade depend upon fat concentration but not schedule of access.

In Vivo Time‐Course Changes in Ethanol Levels Sampled With Subcutaneous Microdialysis

The objective of this study was to determine time-course changes in in vivo ethanol (EtOH) concentrations using a novel subcutaneous (s.c.) microdialysis sampling technique. The hypothesis to be tested was that EtOH concentrations in the s.c. fluid would reflect blood EtOH concentrations. If this is the case, then s.c. microdialysis could allow a more detailed analysis of changes in in vivo levels of EtOH under different drinking paradigms. Adult male and female Wistar rats and male alcohol-preferring (P) rats were used in this study. A loop-style microdialysis probe was designed for s.c. applications. After initial in vitro characterization, probes were implanted under the skin between the shoulder blades. Animals were allowed to recover 4 to 24 hours prior to microdialysis collection (2.0 microl/min flow rate with isotonic saline). In vivo microdialysis experiments were then conducted to determine (i) the extraction fraction (or clearance) using EtOH no-net-flux (NNF) coupled with the alcohol clamp method, (ii) the dose-response and time-course effects after systemic EtOH administration and to compare with blood EtOH levels, and (iii) the time-course changes in EtOH levels during and after an EtOH drinking episode. In vivo probe recovery (extraction fraction) obtained using the alcohol clamp method was 69 +/- 3%, and was comparable to the in vitro recovery of 73 +/- 2%. For the EtOH dose-response experiment, rats injected i.p. with 0.5, 1.0, or 2.0 g/kg EtOH showed a clear dose-response effect in the s.c. dialysate samples. Peak concentrations (70, 123, and 203 mg%, respectively) were reached by 15 minutes after injection. In an experiment comparing levels of EtOH in s.c. dialysis and arterial blood samples in rats administered 1.0 g/kg EtOH, similar time-course changes in in vivo EtOH concentrations were observed with both i.g. and i.p. EtOH administration. In P rats drinking 15% EtOH during a 1-hour scheduled access period, EtOH levels in s.c. microdialysates rose rapidly over the session and peaked at approximately 50 mg% at 60 to 80 minutes. Overall, these experiments indicate that s.c. EtOH and blood EtOH concentrations follow a similar time course. Moreover, s.c. microdialysis can be useful as an experimental approach for determining detailed time-course changes in in vivo EtOH concentrations associated with alcohol drinking episodes.

CP-TDMA: Coloring- and Probability-Based TDMA Scheduling for Wireless Ad Hoc Networks

This paper addresses the issue of transmission scheduling in wireless ad hoc networks. We propose a Time Division Multiple Access (TDMA) scheduling scheme based on edge coloring and probabilistic assignment, called CP-TDMA. We categorize the conflicts suffered by wireless links into two types: explicit conflicts and implicit conflicts, and utilize two different strategies to deal with them. Explicit conflicts are avoided completely by a simple distributed edge-coloring algorithm μ-M, and implicit conflicts are minimized by applying probabilistic time slot assignments to links. We evaluate CP-TDMA analytically and numerically, and find that CP-TDMA, which requires only local information exhibits a better performance than previous work.

Reservation-based protocol for monitoring applications using IEEE 802.15.4 sensor networks

The IEEE 802.15.4 and Zigbee are protocols aimed at low-duty and low-power wireless sensor networks. Continuously monitoring applications such as applications of structural health monitoring could benefit from low power consumption of the IEEE 802.15.4 radio chips. However, existing implementation of IEEE 802.15.4 has limited applicability to 'proactive', high-traffic monitoring sensor networks with constant data streams. In this paper, a Time Division Multiple Access (TDMA) scheduler was designed and implemented to resolve issues with collisions and interference, bandwidth usage and delivery of low latency data in a healthy network and to significantly minimise power consumption by sensor nodes. These improvements maintained compatibility with non-TDMA aware nodes. This scheduler was simulated using Network Simulator-2 for different network scenarios that show a remarkable improvement in the network throughput. The proposed mechanism was also successfully tested and implemented in Wireless Intelligent Sensor and Actuator Network (WISAN).

A game-theoretic analysis of denial of service attacks in wireless random access

In wireless access, transmitter nodes need to make individual decisions for distributed operation and do not necessarily cooperate with each other. We consider a single-receiver random access system of non-cooperative transmitters with the individual objectives of optimizing their throughput rewards, transmission energy costs and delay costs. The non-cooperative transmitter behavior may be purely selfish or may also reflect malicious objectives of generating interference to prevent the successful transmissions of the other nodes as a form of denial of service attack. Our goal is to evaluate the interactions between selfish and malicious nodes that have the dual objectives of optimizing their individual performance measures and blocking the packet transmissions of the other selfish nodes. We assume saturated packet queues of infinite buffer capacities and consider a general multi-packet reception channel that allows packet captures in the presence of simultaneous transmissions. In this context, we formulate a non-cooperative random access game of selecting the individual probabilities of transmitting packets to a common receiver. We derive the non-cooperative transmission strategies in Nash equilibrium. The analysis provides insights for the optimal strategies to block random access of selfish nodes as well as the optimal defense mechanisms against the possible denial of service attacks of malicious nodes in wireless networks. The results are also compared with the cooperative equilibrium strategies that optimize the total system utility (separately under random access and scheduled access). A pricing scheme is presented to improve the non-cooperative operation. For distributed implementation, we formulate a repeated game of the best-response strategy updates and introduce adaptive heuristics (based on the channel feedback only) provided that the system parameters are not explicitly known at the individual transmitters.

Matching daily healthcare provider capacity to demand in advanced access scheduling systems

Advanced access scheduling, introduced in the early 1990s, is reported to significantly improve the performance of outpatient clinics. The successful implementation of advanced access scheduling requires the match of daily healthcare provider capacity with patient demand. In this paper, for the first time a closed-form approach is presented to determine the optimal percentage of open-access appointments to match daily provider capacity to demand. This paper introduces the conditions for the optimal percentage of open-access appointments and the procedure to find the optimal percentage. Furthermore, the sensitivity of the optimal percentage of open-access appointments to provider capacity, no-show rates, and demand distribution is investigated. Our results demonstrate that the optimal percentage of open-access appointments mainly depends on the ratio of the average demand for open-access appointments to provider capacity and the ratio of the show-up rates for prescheduled and open-access appointments.

Efficient Memory Utilization for High-Speed FPGA-Based Hardware Emulators with SDRAMs

FPGA-based hardware emulators are often used for the verification of LSI functions. They generally have dedicated external memories, such as SDRAMs, to compensate for the lack of memory capacity in FPGAs. In such a case, access between the FPGAs and the dedicated external memory may represent a major bottleneck with respect to emulation speed since the dedicated external memory may have to emulate a large number of memory blocks. In this paper, we propose three methods, “Dynamic Clock Control (DCC),” “Memory Mapping Optimization (MMO),” and “Efficient Access Scheduling (EAS),” to avoid this bottleneck. DCC controls an emulation clock dynamically in accord with the number of memory accesses within one emulation clock cycle. EAS optimizes the ordering of memory access to the dedicated external memory, and MMO optimizes the arrangement of the dedicated external memory addresses to which respective memories will be emulated. With them, emulation speed can be made 29.0 times faster, as evaluated in actual LSI emulations.

Open Access Scheduling

Open Access Scheduling

On Joint MAC and Network Coding in Wireless Ad Hoc Networks

This paper addresses network coding in wireless networks in conjunction with medium access control (MAC). It is known that coding over wired networks enables connections with rates that cannot be achieved by routing. However, the properties of wireless networks (e.g., omnidirectional transmissions, destructive interference, single transceiver per node, finite energy) modify the formulation of time-varying network coding in a way that reflects strong interactions with underlying MAC protocols and deviates from the classical approach used in wired network coding. To perform network coding over conflict-free transmission schedules, predetermined network realizations are separately activated by a time-division mechanism and the content of network flows is derived through network coding to optimize performance measures such as achievable throughput and energy costs. A systematic method is presented to construct linear wireless network codes and interactions with MAC schedules are discussed under wireless assumptions. Network coding is also extended to operate with arbitrary (random or scheduled access based) MAC protocols. Alternatively, conflict-free transmission schedules are jointly constructed with network codes by decomposing wireless networks into subtrees and employing graph coloring on simplified subtree graphs. Finally, network coding and plain routing are compared in terms of throughput, energy and delay performance under different MAC solutions.

A Verifiable Language for Programming Real-Time Communication Schedules

Distributed hard real-time systems require predictable communication at the network level and verifiable communication behavior at the application level. At the network level, communication between nodes must be guaranteed to happen within bounded time and one common approach is to restrict the network access by enforcing a time-division multiple access (TDMA) schedule. At the application level, the application's communication behavior should be verified to ensure that the application uses the predictable communication in the intended way. Network code is a domain-specific programming language to write a predictable verifiable distributed communication for distributed real-time applications. In this paper, we present the syntax and semantics of network code, how we can implement different scheduling policies, and how we can use tools such as model checking to formally verify the properties of network code programs. We also present an implementation of a runtime system for executing network code on top of RTLinux and measure the overhead incurred from the runtime system.

Evaluating Complex MAC Protocols for Sensor Networks with APMC

In this paper we present an analysis of a MAC (Medium Access Control) protocol for wireless sensor networks. The purpose of this protocol is to manage wireless media access by constructing a Time Division Media Access (TDMA) schedule. APMC (Approximate Probabilistic Model Checker) is a tool that uses approximation-based verification techniques in order to analyse the behavior of complex probabilistic systems. Using APMC, we approximately computed the probabilities of several properties of the MAC protocol being studied, thus giving some insights about it performance.

Forebrain agouti-related protein (AgRP) injections increase appetitive but not consummatory feeding behaviors in the rat.

Agouti-related protein (AgRP), an endogenous melanocortin receptor inverse agonist, stimulates feeding. Exogenous application promotes ingestion over an extended multi-day period. In the current study, several methods were employed to determine the effects of lateral (LV) or third ventricle (3 V) injections of AgRP on appetitive and consummatory measures of feeding behavior. In Experiment 1, rats were injected with AgRP (1 nM/3 μl) or vehicle into either 3V or LV, 2 h prior to 30 min enclosure in one side of a conditioned place preference test chamber, over 3 consecutive days. On day 4, rats were tested for 30 min place preference. In Experiment 2, rats received LV injection of AgRP/vehicle 2 h prior to 4 h scheduled access to a lick spout containing 0.05 M sucrose. The time of each lick was recorded. In Experiment 1, rats receiving LV but not 3 V AgRP injections exhibited a significant preference for the sided associated with AgRP ( p <0.001). AgRP, LV or 3 V, also significantly increased chow intake over training days ( p <0.05). In Experiment 2, LV AgRP significantly increased 4 h sucrose intake by ∼40% ( p <0.05). This effect was entirely mediated by a comparable increase in meal frequency ( p <0.05). There was no effect of AgRP on any measures of intra-meal microstructure, including average meal size, meal duration, ingestion rate, initial lick rate, or burst size or number. These results are consistent with the finding that AgRP enhances foraging more than feeding in the hamster, while they contrast the effects of hindbrain melanocortin antagonist injections in rat, which were limited to meal size rather than frequency. Together, the results suggest multiple sites of AgRP action on separate aspects of feeding. Supported by NIH DK 59836 and DC 07389.

On the Delta(d)–chromatic number of a complete balanced multipartite graph

In this paper we solve (approximately) the problem of finding the minimum number of colours with which the vertices of a complete, balanced, multipartite graph G may be coloured such that the maximum degrees of all colour class induced subgraphs are at most some specified natural number d. The minimum number of colours in such a colouring is referred to as the Delta(d)–chromatic number of G. The problem of finding the Delta(d)–chromatic number of a complete, balanced, multipartite graph has its roots in an open graph theoretic characterisation problem and has applications conforming to the generic scenario where users of a system are in conflict if they require access to some shared resource. These conflicts are represented by edges in a so–called resource access graph, where vertices represent the users. An efficient resource access schedule is an assignment of the users to a minimum number of groups (modelled by means of colour classes) where some threshold d of conflict may be tolerated in each group. If different colours are associated with different time periods in the schedule, then the minimum number of groupings in an optimal resource access schedule for the above set of users is given by the Delta(d)–chromatic number of the resource access graph. A complete balanced multipartite resource access graph represents a situation of maximum conflict between members of different user groups of the system, but where no conflict occurs between members of the same user group (perhaps due to an allocation of diverse duties to the group members).

Liquid sucrose bingeing in rats depends on the access schedule, concentration and delivery system

Previous studies have reported binge-type consumption of solid vegetable shortening in non-food deprived rats maintained on schedules of limited shortening access. The current study determined if limited access would promote binge-type consumption of sucrose solutions. Adult male rats (6 groups, n = 10 each) were provided with one of three different sucrose concentrations (3.2%, 10%, 32% w/v) for 2 h either everyday (Daily) or Monday, Wednesday, and Friday (Intermittent). A ‘binge’ during the 2-h access periods was operationally defined as Intermittent intakes significantly greater than Daily intakes. Sucrose initially was provided in a 100 ml glass tube equipped with a stainless-steel drinking spout. Under these conditions, there were no differences in sucrose intake between Daily and Intermittent groups at any of the concentrations. In contrast, when sucrose was provided in a modified 60 ml plastic syringe with the same drinking spout, intakes of the Intermittent groups consuming 3.2% and 10% sucrose were greater than those of the respective Daily groups, indicating that binge-type consumption of sucrose occurred. These results demonstrate that brief, intermittent access to low and moderate concentrations of sucrose can promote binge-type behavior, and the characteristics of the drinking apparatus can affect sucrose intake.

Effects of clinical characteristics on successful open access scheduling

Many outpatient clinics are experimenting with open access scheduling. Under open access, patients see their physicians within a day or two of making their appointment request, and long-term patient booking is very limited. The hope is that these short appointment lead times will improve patient access and reduce uncertainty in clinic operations by reducing patient no-shows. Practice shows that successful implementation can be strongly influenced by clinic characteristics, indicating that open access policies must be designed to account for local clinical conditions. The effects of four variables on clinic performance are examined: (1) the fraction of patients being served on open access, (2) the scheduling horizon for patients on longer-term appointment scheduling, (3) provider care groups, and (4) overbooking. Discrete event simulation, designed experimentation, and data drawn from an intercity clinic in central Indiana are used to study the effects of these variables on clinic throughput and patient continuity of care. Results show that, if correctly configured, open access can lead to significant improvements in clinic throughput with little sacrifice in continuity of care.

Radio resource management in HSDPA and HSUPA

This paper discusses the interaction between high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA) scheduling algorithms running in the Node B and other resource management algorithms in the radio network controller (RNC), which are still required to satisfy user-perceived quality. We investigate the effect of load sharing with legacy dedicated channel transmission, and discuss load control algorithms suitable for HSDPA and HSUPA packet transmission. The main concepts of resource allocation are discussed together with results obtained from a dynamic system simulator developed by Alcatel-Lucent. © 2007 Alcatel-Lucent.

Effect of Ethanol on Hypothalamic Opioid Peptides, Enkephalin, and Dynorphin: Relationship With Circulating Triglycerides

Recent evidence has demonstrated that ethanol intake can stimulate the expression and production of the feeding-stimulatory peptide, galanin (GAL), in the hypothalamic paraventricular nucleus (PVN), and that PVN injection of this peptide, in turn, can increase the consumption of ethanol. To test the hypothesis that other feeding-related systems are involved in ethanol intake, this study examined the effect of ethanol on the hypothalamic opioid peptides, enkephalin (ENK), and dynorphin (DYN). Adult, male Sprague-Dawley rats were trained to voluntarily drink increasing concentrations of ethanol, up to 9% v/v, on a 12-hour access schedule or were given a single injection of ethanol (10% v/v) versus saline vehicle. The effect of ethanol on GAL, ENK, and DYN mRNA was measured using real-time quantitative polymerase chain reaction and radiolabeled in situ hybridization, while radioimmunoassay was used to measure peptide levels. In addition to blood alcohol, circulating levels of triglycerides (TG), leptin, and insulin were also measured. The data demonstrated that: (1) rats voluntarily drinking 9% v/v ethanol (approximately 2.0 g/kg/d) show a significant increase in GAL, ENK, and DYN mRNA in the PVN compared with water-drinking rats; (2) voluntary consumption of ethanol also increases peptide levels of ENK and DYN in the PVN; (3) acute injection of 10% ethanol (1.0 g/kg of 10% v/v) similarly increases the expression of GAL, ENK, and DYN in the PVN; and (4) ethanol consumption and injection, while having little effect on leptin and insulin, consistently increase circulating levels of TG as well as alcohol, both of which are strongly, positively correlated with peptide expression in the PVN. These findings, together with published studies, suggest a possible role for hypothalamic opioid peptides in the drinking of ethanol. Based on evidence that dietary fat and lipid injections stimulate the PVN peptides and injection of the opiates and GAL increase ethanol intake, it is proposed that both TG and alcohol in the circulation, which are elevated by the ingestion or injection of ethanol, are involved in stimulating these peptides in the PVN, which in turn promote further consumption of ethanol.

Modified user-dependent perfect-scheduling multiple access protocol for WLAN

Based on effective contention access and perfect scheduling transmission, an enhanced multiple access protocol UPMA++ protocol is proposed. It allocates the resource dynamically according to the actual traffic requirement and does not require the synchronisation in the whole network. This protocol adjusts the length of contention access period and polling period effectively to resolve the conflicts between active stations and transmission stations. By analysis, the optimal contention access period length for the given polling period length is found, and the performance evaluations show that UPMA++ protocol has a high throughput, low average message delay and small average message dropping probability.

Distortion Optimized Packet Scheduling and Prioritization of Multiple Video Streams over 802.11e Networks

This paper presents a generic framework solution for minimizing video distortion of all multiple video streams transmitted over 802.11e wireless networks, including intelligent packet scheduling and channel access differentiation mechanisms. A distortion prediction model designed to capture the multireferenced frame coding characteristic of H.264/AVC encoded videos is used to predetermine the distortion importance of each video packet in all streams. Two intelligent scheduling algorithms are proposed: the “even-loss distribution,” where each video sender is experiencing the same loss and the “greedy-loss distribution” packet scheduling, where selected packets are dropped over all streams, ensuring that the most significant video stream in terms of picture context and quality characteristics will experience minimum losses. The proposed model has been verified with actual distortion measurements and has been found more accurate than the “additive distortion” model that omits the correlation among lost frames. The paper includes analytical and simulation results from the comparison of both schemes and from their comparison to the simplified additive model, for different video sequences and channel conditions.

TEDS: A high speed digital mobile communication air interface for professional users

The TETRA enhanced data service (TEDS) standard has been developed within the Technical Committee TETRA of the European Telecommunications Standards Institute as a major upgrade to the existing narrow-band ETSI TETRA system to supply professional users with high-speed IP packet data services over wireless mobile channels. Multicarrier-based modulation format, powerful payload and header encoding and link adaptation methods are among techniques employed for this purpose. The above enhancements are efficiently combined with improved higher layer protocols enabling a number of new services such as multiple multimedia access with QoS re-negotiation during the session, various priority mechanisms, provision of scheduled access for delay-sensitive applications and support for sectored antenna usage. The aim of this paper is to give a comprehensive overview of the TEDS features with particular emphasis on the physical layer and medium access control features together with representative link and system performance results