Mean wind velocity in an artificially thickened boundary layer

Simulation of wind flow over ditrerent terrains under adiabatic conditions of the atmospheric boundary layer has begin attempted in a wind tunnel moving a velocity profile generator called honeycomb-cum-flat plate (HFP). The HFP was tested in a 10\·v-speed, short test section (0' 61 x O· 61 m), open-circuit wind tunnel. Measurements of mean velocity profiles downstream of HFP, at different speeds of the tunnel, reveal that the artificially generated boundary layer is considerably thick (about 32 to 34 em) and developed at a downstream distance of 2·6 m. The profiles produced at free stream velocities 10-12 mfsec follow closely the power law profiles characteristic of flow, under adiabatic conditions of the atmosphere, over terrain of a levd country with numerous scattered obstructions

Presynaptic facilitation at the crayfish neuromuscular junction: Role of calcium-activated potassium conductance

Membrane potential was recorded intracellularly near presynaptic terminals of the excitor axon of the crayfish opener neuromuscular junction (NMJ), while transmitter release was recorded postsynaptically. This study focused on the effects of a presynaptic calcium-activated potassium conductance, gK(Ca), on the transmitter release evoked by single and paired depolarizing current pulses. Blocking gK(Ca) by adding tetraethylammonium ion (TEA; 5-20 mM) to a solution containing tetrodotoxin and aminopyridines caused the relation between presynaptic potential and transmitter release to steepen and shift to less depolarized potentials. When two depolarizing current pulses were applied at 20-ms intervals with gK(Ca) not blocked, the presynaptic voltage change to the second (test) pulse was inversely related to the amplitude of the first (conditioning) pulse. This effect of the conditioning prepulse on the response to the test pulse was eliminated by 20 mM TEA and by solutions containing 0 mM Ca2+/1 mM EGTA, suggesting that the reduction in the amplitude of the test pulse was due to activation of gK(Ca) by calcium remaining from the conditioning pulse. In the absence of TEA, facilitation of transmitter release evoked by a test pulse increased as the conditioning pulse grew from -40 to -20 mV, but then decreased with further increase in the conditioning depolarization. A similar nonmonotonic relationship between facilitation and the amplitude of the conditioning depolarization was reported in previous studies using extracellular recording, and interpreted as supporting an additional voltagedependent step in the activation of transmitter release. We suggest that this result was due instead to activation of a gK(Ca) by the conditioning depolarization, since facilitation of transmitter release increased monotonically with the amplitude of the conditioning depolarization, and the early time course of the decay of facilitation was prolonged when gK(Ca) was blocked. The different time courses for decay of the presynaptic potential (20 ms) and facilitation (> 50 ms) suggest either that residual free calcium does not account for facilitation at the crayfish NMJ or that the transmitter release mechanism has a markedly higher affinity or stoichiometry for internal free calcium than does g K(Ca). Finally, our data suggest that the calcium channels responsible for transmitter release at the crayfish NMJ are not of the L, N, or T type.This work was partially supported by NIAAA grant AA0776 to G. D. Bittner.Neuroscienc

Steady pressure measurements in the strap-on booster interference Region of 1/20 scale aslv configuration

Wind tunnel studies were carried out to obtain pressure distribution in the strap-on booster interference region of 1/20th scale Augmented Satellite Launch Vehicle model configuration. Tests were done in the 1 .2m tunnel at NAL in the Mach number range of 0 .5 to 2.5 for the clean configuration as well as with spring housing attachments on the strap-on boosters. Both the model configurations with the boosters strapped on to the core vehicle in the horizontal plane (pitch) and in the vertical plane (yaw) were tested for incidences at 0, 4 and -4 deg. In addition pressure measurements were also done on the core vehicle alone at Mach numbers 2.1, 2.5 and 3.0 for 0, +4 degree incidences. The test Reynolds number was varied from 0.7 to 1.3 millions based on the maximum diameter of the model. The pressure distribution showed significant interference effects of boosters on the core vehicle. It is observed that the positive pressure peak associated with flow compression at the flare junction increases with increase in Mach number. In the pitch plane the normal force distribution remains positive along the core vehicle whereas in the yaw plane it is of less magnitude

Physical Metallurgy of Aluminium

Despite the fact that the production is highly energy intensive aluminium and its alloys are the most widely used engineering materials next only to iron and steel because of their functional and economical competi-tiveness. The world over, efforst are on to improve the properties of aluminium/alloys with a view to replacing costly and heavy weight materials in many applications, automobile, space and aerospace for example, for energy saving and economic benifits

An indigenous technology for a silver brazing alloy

This paper deals with the development of an indigenous technology for a widely used silver brazing alloy (BAg-1). Melting, alloying, casting and processing along with the heat treatment schedules, have been dealt with. Particular emphasis has been laid on the corrosion behaviour of this alloy

Role of Thermomechanical Treatments on Mechanical Prope-rties, Microstrucures and Corrosion Properties of Micro-alloyed Steels

The paper deals with the developments in HSLA in general and the effect of thermomechanical processing on mecha-nical properties and corrosion in particular. The effect of micro additions on the properties are also dealt with. It has been pointed out that there is tremendous potential for HSLA for ship building, offshore structures, auto-bodies and many other engineering applications

Fluxes of heat and momentum over sea surface during the passage of ε depression in the north Bay of Bengal

Tims variation of surface Fluxes of heat, moisture and momentum over a sea station (20:N89E) in the norm Bay of Bengal Mas been computed bv srofiie method lor the Period IK;:-, 25th Angus; 1990 using meteorological data of MOSTBL EX-90 from OR Y Sayarkniyii. The fluxes showed synoptic and uiurnal variations nnich ars rrarked during oppression (20th-21st August) comparée to their variation prior to and after tais period. Variations of heal and water vapour fluxes were in phase. Nigh- time fluxes are ralati.eiy high ccmpared to day time. Average ir.orner.tam transfer during depressor. two io three times large. Variations in Bowen ratio wers relatively large during day time. During depression, it varied between 0-2 in day lime and about 00 A., nignt and in the undisturbed period between 0-1 jnd 0-2 during day time and 0-2 and 025 at nigh:. The study shows that the assumption of the exchange coefficients normaiiy used ir. estimating the Ruxes by the buk Lu-rodyr.umic method is not appropriate because Cy/C- C and CH/C14

Reversible Data Hiding scheme using modified Histogram Shifting in Encrypted Images for Bio-medical images

Existing Least Significant Bit (LSB) steganography system is less robust and the stego-images can be corrupted easily by attackers. To overcome these problems Reversible data hiding (RDH) techniques are used. RDH is an efficient way of embedding confidential message into a cover image. Histogram expansion and histogram shifting are effective techniques in reversible data hiding. The embedded message and cover images can be extracted without any distortion. The proposed system focuses on implementation of RDH techniques for hiding data in encrypted bio-medical images without any loss. In the proposed techniques the bio-medical data are embedded into cover images by reversible data hiding technique. Histogram expansion and histogram shifting have been used to extract cover image and bio- medical data. Each pixel is encrypted by public key of Paillier cryptosystem algorithm. The homomorphic multiplication is used to expand the histogram of the image in encrypted domain. The histogram shifting is done based on the homomorphic addition and adjacent pixel difference in the encrypted domain. The message is embedded into the host image pixel difference. On receiving encrypted image with additional data, the receiver using his private key performs decryption. As a result, due to histogram expansion and histogram shifting embedded message and the host image can be recovered perfectly. The embedding rate is increased in host image than in existing scheme due to adjacency pixel difference

Reversible Data Hiding scheme using modified Histogram Shifting in Encrypted Images for Bio-medical images

Existing Least Significant Bit (LSB) steganography system is less robust and the stego-images can be corrupted easily by attackers. To overcome these problems Reversible data hiding (RDH) techniques are used. RDH is an efficient way of embedding confidential message into a cover image. Histogram expansion and histogram shifting are effective techniques in reversible data hiding. The embedded message and cover images can be extracted without any distortion. The proposed system focuses on implementation of RDH techniques for hiding data in encrypted bio-medical images without any loss. In the proposed techniques the bio-medical data are embedded into cover images by reversible data hiding technique. Histogram expansion and histogram shifting have been used to extract cover image and bio- medical data. Each pixel is encrypted by public key of Paillier cryptosystem algorithm. The homomorphic multiplication is used to expand the histogram of the image in encrypted domain. The histogram shifting is done based on the homomorphic addition and adjacent pixel difference in the encrypted domain. The message is embedded into the host image pixel difference. On receiving encrypted image with additional data, the receiver using his private key performs decryption. As a result, due to histogram expansion and histogram shifting embedded message and the host image can be recovered perfectly. The embedding rate is increased in host image than in existing scheme due to adjacency pixel difference