Showing papers by "Ben-Gurion University of the Negev published in 1976"

Algebraic system theory: an analyst's point of view

Abstract: A systematic development of the realization theory of finite dimensional constant linear systems is presented which synthesizes the various currently available approaches. Based on representation theorems for submodules and quotient modules of spaces of polynomial matrices and vectors, this paper combines the abstract algebraic ideas centering around module theory, the use of coprime factorizations of rational transfer functions and state space equations into a unified theory.

Pests as a Common Property Resource: A Case Study of Alfalfa Weevil Control

Abstract: The biological interactions of a pest-plant system are incorporated into an optimal pest-control model, using data and estimated parameters specific to the alfalfa weevil. Due to the externalities inherent in situations involving common property resources, different solutions are obtained for private and societal formulations of the optimization problem. In contrast to current pesticide-spraying practices, it is shown that pesticide should be applied early in the season, before any damage can be observed.

On Partial Equilibrium in a Queuing System with Two Servers

Abstract: This paper will deal with the following question: what happens in a service system where the service is supplied by two competitive firms? By a service system we mean any system where customers have to wait in lines before they are served. As we will show, we cannot apply the usual results of economic theory to service systems. For example, in ordinary economic theory two firms supplying the same good will always sell it at the same price. This result is not always true for the case of service and waiting lines. We will discuss the conditions under which two service firms selling at the same price are not in equilibrium. A discussion of queuing systems with single server (that is, a monopoly) are found in the works of Edelson [1], Naor [3], Knudsen [2] and others. However, there is no mention in the literature of a general equilibrium in a queuing system with more than one server. Between these two extreme cases, the general equilibrium and the determinate single-firm model, lie the partial equilibrium cases, and this paper deals with one of these.

Heat flow, gap formation and break-outs in the continuous casting of steel slabs

Abstract: A theoretical investigation of heat flow and gap formation in the mold of a continuous slab caster has been undertaken using a mathematical model, with the ultimate purpose of predicting the casting conditions which can lead to break-outs. The mathematical model that has been developed for this study is capable of treating the heat flow and air gap as coupled phenomena, and can accept operating variables such as slab size, casting speed, mold taper, and thermal conductivity of the mold powder, as input. Four different cases of slab casting have been investigated; and it has been found that hot spots can form on the surface of the slab within a few centimeters of the corners. Depending on their temperature, it is suggested that these hot spots may give rise to the formation of break-outs off the corners of the slab. From an examination of the behavior of the hot spots, the susceptibility of the cases studied to break-outs has been evaluated. The usefulness of the present analysis in qualitatively ascertaining the location and extent of mold wear under different casting conditions has also been examined.

Dynamic operating rules for motel reservations

Abstract: When customers call a motel or a hotel to reserve a particular room (large, small, suites, single-bed, double-bed, etc.) decisions have to be made concerning the allocation of the available rooms. This paper presents a model for determining the maximum number of specific bookings that should be made for each type of room. The objective is to maximize the expected contribution to profit per rental day. The model considers the distribution of requests for reservations over time as well as cancellations. Also included are the effects of late (unbooked) arrivals and overbookings.

Amelioration of Chilling Injuries in Cucumber Seedlings by Abscisic Acid

Abstract: Exposure of cucumber seedlings (Cucumis sativus L.) to chilling temperature resulted in injuries such as increased leakage of cellular materials, loss of water and wilting. In addition, the development of the seedlings after the exposure to chilling was impaired. Abscisic acid applied to the seedlings prior to chilling significantly ameliorated these injuries.

Feeding, energy flow and soil turnover in the desert isopod, Hemilepistus reaumuri.

Abstract: The desert woodlouse Hemilepistus reaumuri is one of the most abundant macroscopic invertebrates in North Africa, the Arabian steppes, semi-desert and desert, and the Negev desert Israel.The main purposes of our study were: 1. To investigate the feeding behaviour of H. reaumuri in the field and the laboratory, with special attention to the importance of soil and perennials in the isopods' diet. 2. To estimate annual energy flow and soil turnover by the isopods and to relate it to the role of isopods in the desert ecosystem. The results of field observations and feeding experiments in the laboratory show: a) That desert isopods are saprovores, herbivores and microbivores. b) That in order to survive the isopod should include soil particles and or soil minerals when feeding on vegetation. c) Annual ingestion was 10.3-38.6 kcals/m2, 3-12% of the available dead organic matter, and soil turnover 28.5-105.7 g/m2. It was hypothesized that by ingestion and defaecation of organic matter and inorganic soil particles, H. reaumuri alters the structure of the decomposition substrate and increase the rate of decomposition in the desert ecosystem.

Release of platelet 5-hydroxytryptamine by plasma taken from patients during and between migraine attacks.

Abstract: Experiments were carried out in order to further delineate the pathophysiology of the fall of plasma 5-hydroxytryptamine (5-HT) during a migraine attack. Platelets from normal subjects were incubated with 14C-labelled 5-HT, and the release of 5-HT was measured following exposure of these platelets to plasma taken from migraine patients during an attack or at headache-free intervals. Plasma taken during attacks released significantly more 5-HT. It is concluded that factor(s) exist in the serum during migraine attacks, which can cause 5-HT release from normal platelets. The identification of this factor may be important.

Physiology of Polyploid Plants: Water Balance in Autotetraploid and Diploid Tomato under Low and High Salinity

Abstract: Diploid and autotetraploid plants of the cultivated tomato Lycopersicon esculentum cv. Lukullus (Luk) were studied under low and high salinity. Polyploids had a higher water content than diploid plants. Water content in both plant types decreased under salinity, the decrease being smaller in the polyploid plants. Dry weight of whole young plants decreased in both diploid and polyploid plants under salinity, the decrease being smaller in the latter. Transpiration of whole plants, grown in control solution, was lower in polyploid than in diploid plants and decreased more under salinity in the latter. Rate of change of water loss of detached drying leaves was similar in diploid and polyploid plants. Leaves of control diploid plants, however, lost more water per unit leaf area during the phase of stomatal closure apparently due to higher stomatal density. Polyploid plants had fewer but more open stomata per unit leaf area, under both control and saline conditions. Root pressure, determined only under control conditions, seemed to be higher in polyploid plants. No difference in Cl− concentration per unit leaf dry weight was found between diploid and polyploid plants grown in either control or NaCl solution.

Near Resonance vibronic coupling. Isoquinoline

Abstract: The interaction spectrum is considered resulting from the near-resonance coupling of a small number of vibronic levels of two different electronic states. In the simple model proposed, the interactions between the near-resonance states are first explicitly considered and then the off-resonance interactions are treated by perturbation theory. The model is applied to the isoquinoline spectrum and it is shown that for isoquinoline the latter interactions may be safely ignored. Good agreement is achieved between the theoretical and experimental spectra, and many puzzling features, such as the irregular nature of the sequence structure and the ambiguous isotope effects are readily explained. The lowest excited singlet state is the nπ*, and it is located within about 1000 cm−1 of the first excited 1ππ*. Two vibronic levels of the 1nπ* state, corresponding to single quanta of the out-of-plane vibrations, are in near-resonance with the vibrationless 1ππ* level.

Matrix Pade approximants and the Bethe-Salpeter equation of the N-N interaction

Abstract: The problem of which diagrams should be taken for the matrix Pade analysis and for the Bethe-Salpeter equation is discussed. The ''potential'' of the Bethe-Salpeter equation with bare intermediate nucleons is related to the ''potential'' of the Bethe-Salpeter equation with dressed intermediate nucleons. The origin of the differences in recent calculations of the nucleon-nucleon phase shifts based on matrix Pade approximants is discussed. (AIP)

Abnormal glow discharge detection of visible radiation.

Abstract: Extension of abnormal glow discharge detection of electromagnetic radiation to visible wavelengths is observed with inexpensive commercial indicator lamps. The spectral response and mechanisms of detection are discussed and advantages over gas-filled photodiodes noted. Responses from different discharge regions are observed and their implications considered.

Selection of the optimal setup policy

Abstract: A model is developed taking into consideration all the costs (namely cost of sampling, cost of not detecting a change in the process, cost of a false indication of change, and the cost of readjusting detected changes) incurred when a production process, using an unscheduled setup policy, utilizes fraction-defective control charts to control current production. The model is based on the concept of the expected time between detection of changes calling for setups. It is shown that the combination of unscheduled setups and control charts can be utilized in an optimal way if those combinations of sample size, sampling interval, and extent of control limits from process average are used that provide the minimum expected total cost per unit of time. The costs of a production process that uses unscheduled setups in conjunction with the appropriate optimal control charts are compared to the costs of a production process that uses scheduled setups at optimum intervals in conjunction with its appropriate control charts. This comparison indicates the criteria for selecting production processes with scheduled setups using optimal setup intervals over unscheduled setups. Suggestions are made to evaluate the optimal process setup strategy and the accompanying optimal decision parameters, for any specific cost data, by use of computer enumeration. A numerical example for assumed cost and process data is provided.

Subnormal Glow Discharge Detection of Optical and Microwave Radiation

Abstract: Commercial indicator lamp glow discharge tubes in the subnormal glow mode exhibit variable frequency tuned filter video response to optical and microwave radiation. Sensitivity to optical radiation can be particularly increased by using such devices in the subnormal rather than abnormal glow. These phenomena are discussed in terms of physical electronics and an equivalent circuit. A comparison is made of abnormal and subnormal glow mode properties. It is hoped that this model can lead to glow discharge lamp design for specific circuit applications involving subnormal glow mode characteristics. Relationships between glow discharge detector physical and electronic parameters are derived.

Dynamic stabilization of tuned-circuit levitators

Abstract: Recent investigations of a relatively new magnetic levitation device are described. This device uses an electromagnet, which is the inductive part of a resonant circuit. If the circuit is properly tuned, static stability is attainable. Levitators built on these lines are simple and reliable. However, it is already well known that a tuned circuit electromagnet on its own is usually not sufficient to maintain levitation for long periods of time, and the suspended object tends to be dynamically unstable. This dynamic instability is prevented by introducing simple electronic or mechanical modifications into the tuned circuit system. Such modifications are described and their investigation is dealt with. The electronic method of stabilization is successfully analyzed by employing the viewpoint of slowly varying quantities. It is believed that the present article is the first to suggest mechanical methods for introducing dynamic stabilization to levitators. It is interesting that mechanical stabilization is achieved without a necessity of employing direct mechanical contact, and the levitated object is suspended freely. The system is stabilized by electromechanically coupling an aluminium solid object to the main levitator circuit.

An empirical model of net photosynthesis for the desert plant Hammada scoparia (Pomel) Iljin

Abstract: An empirical model for describing daily courses of net photosynthesis in Hammada scoparia is being developed. The model is based on the functional relationships, by which various environmental factors affect the photosynthetic activity and which can be measured by experiment in the field. In a sequence of steady-states daily courses of net photosynthesis are predicted during a growing season considering the variability of the physiological states and the capacity for regulative adaptations. The rate of net photosynthesis at a certain date is calculated from the maximal rate of CO2 uptake being expected at that season and from the effects of light, temperature, and air humidity which are scaled from 0 to 1. All factors are connected multiplicatively. The light function accounts for the seasonal changes in the light curve, the temperature function is based on the seasonal shift of the temperature optimum, and the humidity function considers the increasing sensitivity of the stomatal humidity response at increasing water stress. The model is built to be a submodel of a general ecosystem model, where various other submodels (i.e. water stress model, phenology model) are supplied. The present model is tested by predicting daily courses at extreme climatic conditions during the year and by comparing the predicted values of gas exchange with values being measured in an independent experimental procedure. The result shows that the model is able to simulate the natural behaviour of Hammada scoparia during the growing and dry season of a desert habitat. The problems of incorporating the influence of water stress, the interaction of the various factors, and the phenological aspect of the photosynthetic activity is being discussed.