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Search Results: 1 - 10 of 144641 matches for " Tanvir F Choudhri "
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The baboon (Papio anubis) extracranial carotid artery: An anatomical guide for endovascular experimentation
J Mocco, Daniel J Hoh, M Nathan Nair, Tanvir F Choudhri, William J Mack, Ilya Laufer, E Sander Connolly
BMC Cardiovascular Disorders , 2001, DOI: 10.1186/1471-2261-1-4
Abstract: We characterized the extracranial carotid system often male baboons (Papio anubis, range 15.1–28.4 kg) by early post-mortem dissection. Photographic documentation of vessel lengths, lumen diameters, and angles of origin were measured for each segment of the carotid bilaterally.The common carotid arteries averaged 94.7 ± 1.7 mm (left) and 87.1 ± 1.6 mm (right) in length. The average minimal common carotid lumen diameters were 3.0 ± 0.3 mm (left) and 2.9 ± 0.2 mm (right). Each animal had a common brachiocephalic artery arising from the aorta which bifurcated into the left common carotid artery and right braciocephalic artery after 21.5 ± 1.6 mm. The vascular anatomy was found to be consistent among animals despite a wide range of animal weights.The consistency in the Papio anubis extracranial carotid system may promote the use of this species in the preclinical investigation of neuro-interventional therapies.There has been a recent interest in developing aggressive interventional strategies for the treatment of a variety of neurological diseases including stroke, subarachnoid hemorrhage, and head trauma [1-4]. Successful translation of these therapies to the clinical arena, however, is critically dependent on the use of appropriate experimental models [5]. Non-human primate models of neurological diseases currently exist and have the advantage of most closely mimicking human physiology [6]. These models are particularly relevant to neuro-interventional research in that anatomical similarities permit routine vascular access and evaluation of devices designed on a clinically relevant scale.Conducting experimental primate endovascular studies, however, requires a comprehensive understanding of the carotid vascular system. Previous investigations of non-human primate vascular anatomy have focused primarily on the general morphology of the vessels and not on vessel angles, lengths, or lumen diameters which are necessary for guiding endovascular technology [7,8]. To answer
Anomalous Hardening of Submicron Porous Silver at High Strain Rates
Alan F Jankowski,Tanvir Ahmed
Journal of Materials Science Research , 2012, DOI: 10.5539/jmsr.v1n3p76
Abstract: Microscratch hardness measurements were conducted on porous silver membranes using a sphero-conical Rockwell indenter over a strain rate range of 10-1-10+4 s-1. At high strain rates, the porous silver has a strain-rate sensitivity of hardness that is enhanced in comparison to its dense counterpart. The enhancement is found to increase for strain rates greater than 10+2 s-1 wherein strain rate exponents are measured as high as 0.25. The increase appears attributable to the free volume available for deformation within the porous structure. This result represents up to a five-fold increase in the exponent value in comparison to tensile tests conducted at strain rates less than 10-1 s-1.
Distances to Cepheid Open Clusters Via Optical and K-Band Imaging
F. Hoyle,T. Shanks,N. R. Tanvir
Physics , 2000, DOI: 10.1046/j.1365-8711.2003.06939.x
Abstract: We investigate the reddening and Main Sequence fitted distances to eleven young, Galactic open clusters that contain Cepheids. Each cluster contains or is associated with at least one Cepheid variable star. Reddening to the clusters is estimated using the U-B:B-V colours of the OB stars and the distance modulus to the cluster is estimated via B-V:V and V-K:V colour-magnitude diagrams. By main-sequence fitting we proceed to calibrate the Cepheid P-L relation and find M_V=-2.81xlogP-1.33 +/-0.32 and M_K=-3.44xlogP-2.20 +/-0.29 and a distance modulus to the LMC of 18.55+/-0.32 in the V-band and 18.47+/-0.29 in the K-band giving an overall distance modulus to the LMC of 18.51+/-0.3. In the case of two important clusters we find that the U-B:B-V diagram in these clusters is not well fitted by the standard Main Sequence line. In one case, NGC7790, we find that the F stars show a UV excess which if caused by metallicity would imply Fe/H ~ -1.5; this is anomalously low compared to what is expected for young open clusters. In a second case, NGC6664, the U-B:B-V diagram shows too red U-B colours for the F stars which in this case would imply a higher than solar metallicity. If these effects are due to metallicity then it would imply that the Cepheid PL(V) and PL(K) zeropoints depend on metallicity according to delta(M)/delta(Fe/H) ~0.66 in the sense that lower metallicity Cepheids are intrinsically fainter. Medium-high resolution spectroscopy for the main-sequence F stars in these two clusters is needed to determine if metallicity really is the cause or whether some other explanation applies.
On the Tapping Mode Measurement for Young’s Modulus of Nanocrystalline Metal Coatings
H. S. Tanvir Ahmed,Eric Brannigan,Alan F. Jankowski
Journal of Nanotechnology , 2013, DOI: 10.1155/2013/761031
Abstract: Young’s modulus of nanocrystalline metal coatings is measured using the oscillating, that is, tapping, mode of a cantilever with a diamond tip. The resonant frequency of the cantilever changes when the diamond tip comes in contact with a sample surface. A Hertz-contact-based model is further developed using higher-order terms in a Taylor series expansion to determine a relationship between the reduced elastic modulus and the shift in the resonant frequency of the cantilever during elastic contact between the diamond tip and sample surface. The tapping mode technique can be used to accurately determine Young’s modulus that corresponds with the crystalline orientation of the sample surface as demonstrated for nanocrystalline nickel, vanadium, and tantalum coatings. 1. Introduction A variety of indentation-based test methods are used to evaluate strengthening effects [1–4] in materials at the nanoscale. Nanoindentation normal to the surface is routinely used to measure the hardness and Young’s modulus. Triboindentation tests are used [5–7] to measure both hardness and shear strength as well as quantify strain-rate sensitivity [8, 9] effects in the evaluation of deformation mechanisms in nanocrystalline alloys. The standard approach [10–12] to determine the elastic modulus during nanoindentation evaluates the load ( ) versus displacement ( ) curve during unloading after plastic deformation. It remains difficult to collect a sufficient quantity of versus data during elastic loading since elastic displacements ( ) are commonly limited to depths of only a few nanometers or less in many hard materials. The initial linear slope ( ) of the power-law-shaped unloading curve is used [11, 12] to determine the reduced elastic modulus ( ) as The contact area ( ) equals the square of the contact depth ( ) multiplied by the tip area ( ) coefficient, and the shape parameter equals 1.00 for flat punch, 1.034 for Berkovich, and 1.012 for Vickers indenter tips. The reduced elastic modulus ( ) of the indenter tip and sample surface system is related to the elastic moduli of the indenter tip and sample surface as Here, the subscripts and represent the probe tip and sample, respectively, for the Poisson ratio ( ) and Young’s modulus ( ) values. Indentation size effects (ISEs) are found with the directional loading of the indenter tip. For example, beyond an indentation depth, that is, 10% of the film thickness, the use of a Meyer plot indicates [13, 14] that the substrate material contributes to the elastic and plastic property measurements of the coating. Also, the sensitivity
Cepheid, Tully-Fisher and SNIa Distances
T. Shanks,P. D. Allen,F. Hoyle,N. R. Tanvir
Physics , 2002,
Abstract: We first discuss why the uncomfortable fine-tuning of the parameters of the Lambda-CDM cosmological model provides continuing, strong motivation to investigate Hubble's Constant. Then we review evidence from the HST Key Project that there is a significant scale error between raw Cepheid and Tully-Fisher distances. An analysis of mainly HST Distance Scale Key Project data shows a correlation between host galaxy metallicity and the rms scatter around the Cepheid P-L relation, which may support a recent suggestion that the P-L metallicity dependence is stronger than expected. If Cepheids do have a significant metallicity dependence then the Tully-Fisher scale error increases and the distances of the Virgo and Fornax clusters extend to more than 20Mpc, decreasing the value of Ho. Finally, if the Cepheids have a metallicity dependence then so do Type Ia Supernovae since the metallicity corrected Cepheid distances to eight galaxies with SNIa would then suggest that the SNIa peak luminosity is fainter in metal poor galaxies, with important implications for SNIa estimates of qo as well as Ho.
Cepheid and SNIa Distance Scales
T. Shanks,P. D. Allen,F. Hoyle,N. R. Tanvir
Physics , 2001,
Abstract: We first discuss why there remains continuing, strong motivation to investigate Hubble's Constant. Then we review new evidence from an investigation of the Galactic Open Clusters containing Cepheids by Hoyle et al. that the metallicity dependence of the Cepheid P-L relation is stronger than expected. This result is supported by a new analysis of mainly HST Distance Scale Key Project data which shows a correlation between host galaxy metallicity and the rms scatter around the Cepheid P-L relation. If Cepheids do have a significant metallicity dependence then an already existing scale error for Tully-Fisher distances becomes worse and the distances of the Virgo and Fornax clusters extend to more than 20Mpc, decreasing the value of H_0. Finally, if the Cepheids have a metallicity dependence then so do Type Ia Supernovae since the metallicity corrected Cepheid distances to eight galaxies with SNIa now suggests that the SNIa peak luminosity is fainter in metal poor galaxies. As well as having important implications for H_0, this would also imply that the evidence for a non-zero cosmological constant from the SNIa Hubble Diagram may be subject to corrections for metallicity which are as big as the effects of cosmology.
Total Quality Management in Classroom at University Level in Islamabad City
Tanvir Kayani
Pakistan Journal of Commerce and Social Sciences , 2012,
Abstract: The progress of a country inter-depends on the quality of education provided to its citizens. Higher level Education is the most important stage in education system of any country. This stage provides educated graduates and skilled workers that immediatelyenters into the practical field and takes over the responsibilities. That is why to increase the quality of education at this stage is the foremost mission of all the countries. By defining the term, quality is the level of satisfaction for which the consumer pays. In thecase of education, the Consumer is the student as well as society. Therefore, quality education is the standard of education that satisfies the students and society both. The main objectives of this study were to identify the indicators of Total Quality Management(T.Q.M) in classroom to study the efforts of teachers to ensure TQM in classroom and to identify the ways to improve the quality of education at higher level.From the findings of the study it was revealed that the teachers did not covered the five standards of TQM elements completely, students were not completely satisfied by the teaching methodology during knowledge transitory process. Most of the teachers were not prepared before delivering there lectures, teacher showed biasness that discouraged the students. Teacher also ignored the daily assessment of the students, and use of the audio visual (AV) aids in classroom, obsolete teaching material, and ineffective material caused failure to produce total quality education, and failed to produce skilled workforce. Based upon the conclusion of the study it is recommended that teacher may be punctual, teacher should use AV aids for teaching in classroom, teachers may be prepared well before delivering the lecture, teacher may encourage the classroom discussion, andteacher may treat equally in classroom.
Pan’s Labyrinth: The Labyrinth of History
Kuhu Tanvir
Wide Screen , 2009,
Abstract: Capturing history, or interpreting it, has meant many things over the years, ranging from melodrama-driven accounts, to brutally realist narratives to absurdist ‘fragmented’, ‘non-stories’. This paper deals with Guillermo del Torro’s use of the fantastic in Pan’s Labyrinth to allegorise the Spanish Civil War on the one hand, but more importantly, to explore and expand the field of the historical narrative in cinema.
Performance Evaluation of the Layered Space-Time Receiver Using the QR Detection Method
Tanvir Ahmed
International Journal on Computer Science and Engineering , 2012,
Abstract: The conventional V-BLAST detection is a single flow algorithm that consists of the two major operations: 1) the finding of the ordering index and 2) the nulling and symbol cancellation process. Thispaper focuses on the second operation and provides an alternative way for the nulling and symbol cancellation process using the QR decomposition to modify the V-BLAST algorithm for another way ofeffective detection. The decomposition of the channel matrix into the orthonormal matrix Q and the triangular matrix R have created a way of achieving symbol cancellation by means of backward substitution. Results are presented for various system configurations that demonstrate the performance of rearranging the channel matrix using the proposed method as compared to random ordering.
On the Lego-Teichmuller game for finite $G$ cover
Tanvir Prince
Mathematics , 2007,
Abstract: Given a smooth, oriented, closed surface $\Sigma$ of genus zero, possibly with boundary, let $\tilde{\Sigma} \longrightarrow \Sigma$ be a given $G$-cover of $\Sigma$, where $G$ is a given finite group. Let $S_{n}$ denote the standard sphere with $n$ holes. There are many ways of gluing together several $G$-cover of $S_{n}$ to construct the $G$-cover $\ts \longrightarrow \Sigma$, of $\Sigma$. We let $M(\tilde{\Sigma} ,\Sigma)$ be the set of all ways to construct the given $G$-cover, $\tilde{\Sigma} \longrightarrow \Sigma$, of $\Sigma$ from gluing of several $G$-covers of $S_{n}$, here $n$ may vary. In this paper, we define some simple moves and relation which will turn $M(\tilde{\Sigma} ,\Sigma)$ into a connected and simply-connected complex. This will be used in the future paper to construct $G$-equivariant Modular Functor. This $G$-equivariant Modular Functor will be an extension of the usual Modular Functor.
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