MAC Model Research Articles

Vaccine protection from CD4+ T-cell loss caused by simian immunodeficiency virus (SIV) mac251 is afforded by sequential immunization with three unrelated vaccine vectors encoding multiple SIV antigens.

Candidate human immunodeficiency virus (HIV) vaccine strategies that induce strong cellular immune responses protect rhesus macaques that are infected with recombinant simian/human immunodeficiency virus SHIV89.6p from acute CD4+ T-cell loss and delay progression to AIDS. However, similar strategies have not proven as efficacious in the simian immunodeficiency virus (SIV)mac model of AIDS, an infection that causes a slow, steady loss of CD4+ T-cell function and numbers in rhesus macaques similar to that caused by HIV-1, the principal cause of AIDS in humans. Efforts to increase vaccine efficacy by repeated boosting with the same vector are quickly limited by rising anti-vector immune responses. Here, the sequential use of three different vectors (DNA, Semliki Forest virus and modified vaccinia virus Ankara) encoding the same SIVmac structural and regulatory antigens was investigated and demonstrated to prevent or slow the loss of CD4+ T-cells after mucosal challenge with the highly pathogenic SIVmac251 strain. Of particular interest was an inverse association between the extent of T-helper 2 cytokine responses and steady-state virus load. Although limited in the number of animals, this study provides important proof of the efficacy of the triple-vector vaccine strategy against chronic, progressive CD4+ T-cell loss in the rigorous SIVmac/rhesus macaque model of AIDS.

Evaluation of Contention-Based EDCA for IEEE 802.11e Wireless LAN

The legacy IEEE 801.11 doesn’t support QoS streams with priorities. It since causes some QoS demanding applications such as VoIP, Video streaming to be limited in its usefulness. Enhancements have been made to the MAC layer by the new 802.11e standard to support prioritized and parameterized QoS. The work of this paper is to simulate the new scheme and modify the existing OPNET WLAN MAC model to satisfy the 802.1le standard. The modification includes adding four access category queues, AP beacon with EDCA parameters, AC queue switcher and an internal collision handler to evaluate the contention-based channel access mechanism, called enhanced distributed coordination access (EDCA) in the current 802.1le. The performance of those new schemes has been compared with DCF of the 802.11 standard via simulation results. It clearly indicates the IEEE 802.11 EDCA function can effectively provide QoS differentiation.

Interference evaluation of Bluetooth and IEEE 802.11b systems

The emergence of several radio technologies, such as Bluetooth and IEEE 802.11, operating in the 2.4 GHz unlicensed ISM frequency band, may lead to signal interference and result in significant performance degradation when devices are colocated in the same environment. The main goal of this paper is to evaluate the effect of mutual interference on the performance of Bluetooth and IEEE 802.11b systems. We develop a simulation framework for modeling interference based on detailed MAC and PHY models. First, we use a simple simulation scenario to highlight the effects of parameters, such as transmission power, offered load, and traffic type. We then turn to more complex scenarios involving multiple Bluetooth piconets and WLAN devices.

Performance comparison of two on-demand routing protocols for ad hoc networks

Ad hoc networks are characterized by multihop wireless connectivity, frequently changing network topology and the need for efficient dynamic routing protocols. We compare the performance of two prominent on-demand routing protocols for mobile ad hoc networks: dynamic source routing (DSR) and ad hoc on-demand distance vector routing (AODV). A detailed simulation model with MAC and physical layer models is used to study interlayer interactions and their performance implications. We demonstrate that even though DSR and AODV share similar on-demand behavior, the differences in the protocol mechanics can lead to significant performance differentials. The performance differentials are analyzed using varying network load, mobility, and network size. Based on the observations, we make recommendations about how the performance of either protocol can be improved.

Evaluation of Insecticides Against Lepidopterous Pests During Bloom on Blueberries, 1995

Abstract This study was conducted in a ‘Bluecrop’ blueberry field in full production near Whitesbog, NJ. Blueberry bushes were approximately 5 ft tall and spaced 9X4 ft apart. Treatments were arranged in a RCB design, replicated 5 times with each replication consisting of 6 bushes in 2 rows. Two unsprayed rows between blocks and 5 unsprayed bushes between treatments within a block served as buffers. Insecticides were applied with a Mighty Mac model PS-322T garden sprayer equipped with a handgun calibrated to deliver 200 gal/acre at 75 PSI. Insecticides were applied once on 16 May approximately at 50% bloom. GM eggmasses were obtained from USDA-APHIS facility at Otis Air Base in Cape Cod, MA, to augment larval populations in the field plots. Eggmasses were stapled to the bush on 3 May at the rate of 1 eggmass per bush. Eggmasses began to hatch on 6 May and larvae were well distributed on the bushes within a week after hatching. Larval populations were assessed by sampling 25 clusters from each of 4 randomly selected bushes/replicate for a total of 100 leaf and flower clusters/replicate on 15 May (pre-treatment count) and 26 May (post-treatment count). Leaf and flower clusters were randomly selected from the top, middle and bottom thirds of each bush.

Application of enhanced LQG/LTR for distillation control

O'Dell and Misawa (1995) proposed a modification to the traditional LQG/LTR design procedure which provides uniform singular values across all frequencies for the target loop. The modification is easy to implement and significantly improves the performance of the LQG/LTR compensator. This article explores applicability of the technique for distillation column control, the most common multivariable control problem in the process industries. When applied to the Wood/Berry column (1973), performance of the enhanced LQG/LTR compensator is found to be comparable to a MAC model predictive controller and significantly better than traditional SISO PI control. Despite the lack of guaranteed performance and robust stability for nonlinear, nonminimum phase plants, the results suggest further consideration of enhanced LQG/LTR for application in the process industries.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Insecticide Evaluations Against Foliar and Fruit Feeding Insects on Blueberries, 1994

Abstract This experiment was conducted in a recently abandoned ‘bluecrop’ blueberry field in full production, near Whitesbog, NJ. Blueberry bushes were approximately 5 ft tall and spaced 9 × 4 ft apart. Treatments were replicated 6 times in a randomized complete block design with each replicate consisting of 6 bushes in 2 rows. There were 2 unsprayed rows between blocks, and 3 unsprayed bushes between treatments within a block that served as buffer. Insecticides were sprayed to runoff with a Mighty Mac model PS-322T garden sprayer equipped with a Hamilton handgun operated at 200 psi. Approximately 1.25 to 1.5 gal of spray solution was applied per replicate (250-300 gal/acre). Insecticides were applied 3 times beginning petal-fall on 31 May, 10 June, and 23 June. Data were collected from 100 leaf and fruit cluster (CL) samples (25 clusters × 4 randomly selected bushes/replicate) on 8 June and 14 June. Samples consisted of 40 fruit clusters (10 fruit clusters × 4 randomly selected bushes/replicate) on 1 July. A leaf or fruit cluster was considered damaged if at least 1 leaf or fruit in that cluster was injured.

Estimating solar irradiance and components

The performance of models to estimate solar irradiance and its components is assessed using data for six Canadian stations for nine years (1968–1976). Greatest emphasis is placed on a model, the MAC model, which uses cloud information from different layers. Here, effects on model estimates of using observed cloud layer opacities instead of amounts is examined because after 1976 the latter quantity is no longer recorded. Effects of aerosol are also examined. Two other models are considered here; a version of the MAC model which uses total cloud information rather than layer information, and Rietveld's[1] sunshine-based model. In general, the layer model yielded the best results. This is in agreement with a previous Canadian study[2]. RMSE values are between 11 and 15 percent for global irradiance on a daily basis and decrease below 10 percent for averaging periods greater than 2–4 days. Daily RMSE values for the direct beam and diffuse components are 25 per cent. These decrease below 10 per cent for averaging periods larger than 10–15 days. Errors increase when layer opacities are used but results are still acceptable. Aerosol effects can be neglected for much of the country except in Montreal and Toronto. Rietveld's model gives results of lower accuracy than the MAC model but may be useful for quick, easy estimates. The MAC model using total cloud amount performed poorly.