Diffraction of fast atoms and molecules from surfaces

Prompted by recent experimental developments, a theory of surface scattering of fast atoms at grazing incidence is developed. The theory gives rise to a quantum mechanical limit for ordered surfaces that describes coherent diffraction peaks whose thermal attenuation is governed by a Debye-Waller factor, however, this Debye-Waller factor has values much larger than would be calculated using simple models. A classical limit for incoherent scattering is obtained for high energies and temperatures. Between these limiting classical and quantum cases is another regime in which diffraction features appear that are broadened by the motion in the fast direction of the scattered beam but whose intensity is not governed by a Debye-Waller factor. All of these limits appear to be accessible within the range of currently available experimental conditions.Comment: 37 pages including 3 figure

Hexagonal Honeycomb Sandwich Plate Optimization Using Gravitational Search Algorithm

Honeycomb sandwich panels are increasingly used in the construction of space vehicles because of their outstanding strength, stiffness and light weight properties. However, the use of honeycomb sandwich plates comes with difficulties in the design process as a result of the large number of design variables involved, including composite material design, shape and geometry. Hence, this work deals with the presentation of an optimal design of hexagonal honeycomb sandwich structures subjected to space environment. The optimization process is performed using a set of algorithms including the gravitational search algorithm (GSA). Numerical results are obtained and presented for a set of algorithms. The results obtained by the GSA algorithm are much better compared to other algorithms used in this study

Hexagonal Honeycomb Sandwich Plate Optimization Using Gravitational Search Algorithm

Honeycomb sandwich panels are increasingly used in the construction of space vehicles because of their outstanding strength, stiffness and light weight properties. However, the use of honeycomb sandwich plates comes with difficulties in the design process as a result of the large number of design variables involved, including composite material design, shape and geometry. Hence, this work deals with the presentation of an optimal design of hexagonal honeycomb sandwich structures subjected to space environment. The optimization process is performed using a set of algorithms including the gravitational search algorithm (GSA). Numerical results are obtained and presented for a set of algorithms. The results obtained by the GSA algorithm are much better compared to other algorithms used in this study

Hexagonal Honeycomb Sandwich Plate Optimization Using Gravitational Search Algorithm

Honeycomb sandwich panels are increasingly used in the construction of space vehicles because of their outstanding strength, stiffness and light weight properties. However, the use of honeycomb sandwich plates comes with difficulties in the design process as a result of the large number of design variables involved, including composite material design, shape and geometry. Hence, this work deals with the presentation of an optimal design of hexagonal honeycomb sandwich structures subjected to space environment. The optimization process is performed using a set of algorithms including the gravitational search algorithm (GSA). Numerical results are obtained and presented for a set of algorithms. The results obtained by the GSA algorithm are much better compared to other algorithms used in this study

Hexagonal Honeycomb Sandwich Plate Optimization Using Gravitational Search Algorithm

Honeycomb sandwich panels are increasingly used in the construction of space vehicles because of their outstanding strength, stiffness and light weight properties. However, the use of honeycomb sandwich plates comes with difficulties in the design process as a result of the large number of design variables involved, including composite material design, shape and geometry. Hence, this work deals with the presentation of an optimal design of hexagonal honeycomb sandwich structures subjected to space environment. The optimization process is performed using a set of algorithms including the gravitational search algorithm (GSA). Numerical results are obtained and presented for a set of algorithms. The results obtained by the GSA algorithm are much better compared to other algorithms used in this study

A Three-Dimensional TLM Simulation Method for Thermal Effect in PV-Solar Cells

Temperature rising is a negative factor in almost all systems. It could cause by self heating or ambient temperature. In solar photovoltaic cells this temperature rising affects on the behavior of cells. The ability of a PV module to withstand the effects of periodic hot-spot heating that occurs when cells are operated under reverse biased conditions is closely related to the properties of the cell semi-conductor material. In addition, the thermal effect also influences the estimation of the maximum power point (MPP) and electrical parameters for the PV modules, such as maximum output power, maximum conversion efficiency, internal efficiency, reliability, and lifetime. The cells junction temperature is a critical parameter that significantly affects the electrical characteristics of PV modules. For practical applications of PV modules, it is very important to accurately estimate the junction temperature of PV modules and analyze the thermal characteristics of the PV modules. Once the temperature variation is taken into account, we can then acquire a more accurate MPP for the PV modules, and the maximum utilization efficiency of the PV modules can also be further achieved. In this paper, the three-Dimensional Transmission Line Matrix (3D-TLM) method was used to map the surface temperature distribution of solar cells while in the reverse bias mode. It was observed that some cells exhibited an inhomogeneity of the surface temperature resulting in localized heating (hot-spot). This hot-spot heating causes irreversible destruction of the solar cell structure. Hot spots can have a deleterious impact on the total solar modules if individual solar cells are heated. So, the results show clearly that the solar cells are capable of self-generating considerable amounts of heat that should be dissipated very quickly to increase PV module's lifetime

Valorization of fine bran of Algerian durum wheat varieties in the diet of ruminants

The feed value of the fine bran of durum wheat varieties cultivated in Algeria have as characteristics an average content of total nitrogen of 13.2% of dry matter (DM), a fat content of 2.4% of DM and minerals content of 2.8% of DM. These various chemical compounds values confer less fodder units and digestible proteins than those of durum wheat fine bran from Europeans varieties

Valorization of fine bran of Algerian durum wheat varieties in the diet of ruminants

La valeur nutritive des sons fins des variétés de blé dur cultivées en Algérie a pour caractéristiques une teneur moyenne en matières azotées totales de 13,2 % de matière sèche (MS), un taux de matière grasse de 2,4 % de MS et une teneur en matière minérale de 2,8 % de MS. Ces différents composés chimiques leurs confèrent des valeurs en unités fourragères et en protéines digestibles moins importantes que celles des sons fins des blés durs européens. Mots-clés: Alimentation des ruminants, son fin de blé dur algérien, valeur nutritive.The feed value of the fine bran of durum wheat varieties cultivated in Algeria have as characteristics an average content of total nitrogen of 13.2% of dry matter (DM), a fat content of 2.4% of DM and minerals content of 2.8% of DM. These various chemical compounds values confer less fodder units and digestible proteins than those of durum wheat fine bran from Europeans varieties.Keywords: Food of the ruminants, Fine bran of Algerian durum wheat, Feed value