Shafiq Ahmad - Academia.edu (original) (raw)

Papers by Shafiq Ahmad

$Research paper thumbnail of A comparative study of multifractal moments in relativistic heavy-ion collisions$

Journal of Physics G-nuclear and Particle Physics, 2006

A study of the fractal structure of relativistic shower particles produced in the interactions of... more A study of the fractal structure of relativistic shower particles produced in the interactions of 28Si and 12C nuclei at 4.5 A GeV/c with nuclear emulsion using the methods of Takagi moments, Tq, factorial moments, Fq, and modified multifractal moments, Gq, has been performed. The dependences of these moments on the number of bins M are found to follow power law behaviour for the experimental data in pseudorapidity phase space. The calculated values of the generalized fractal dimensions, Dq, are found to decrease with the increasing order of moments, q. This observation indicates the existence of multifractality and a self-similar cascade mechanism in multiparticle production. The multifractal Bernoulli representation Dq = D∞ + c ln q/(q - 1) is found to support the linear dependence of Dq on ln q/(q - 1). Finally, from the analysis of the data it can be concluded that no universality in the values of the multifractal specific heat, c, calculated from Tq, Fq and Gq moments is found. Some consistency seems to be observed in the values of the specific heat obtained from the Takagi method.

In today's ultra competitive business environment, it is becoming more critical than ever to asse... more In today's ultra competitive business environment, it is becoming more critical than ever to assess precisely process losses due to non-compliance of customer specifications. To assess these losses, industry is widely using process capability indices for performance evaluation of their processes. Determination of the performance capability of a stable process using the standard process capability indices (Cp, Cpk) requires that the quality characteristics of the underlying process data should follow a normal distribution. Departures from this normality assumption could lead to erroneous results when applying conventional statistical capability measures which are based on the assumption. Many researchers have been investigating solutions to the non-normality problem. This paper explores application of an innovated method (Pei-His Liu and Fei-Long Chen, 2006) based on Burr distribution for process capability index (PCI) calculations when the quality characteristics data is not normal. A simulation study using gamma distribution is conducted and simulation results are then compared with the commonly used Clements' method. Finally, a case study based on the proposed method will be presented using real data

International Journal of Advanced Manufacturing Technology, 2009

Estimating the process capability index (PCI) for non-normal processes has been discussed by many... more Estimating the process capability index (PCI) for non-normal processes has been discussed by many researches. There are two basic approaches to estimating the PCI for non-normal processes. The first commonly used approach is to transform the non-normal data into normal data using transformation techniques and then use a conventional normal method to estimate the PCI for transformed data. This is a straightforward approach and is easy to deploy. The alternate approach is to use non-normal percentiles to calculate the PCI. The latter approach is not easy to implement and a deviation in estimating the distribution of the process may affect the efficacy of the estimated PCI. The aim of this paper is to estimate the PCI for non-normal processes using a transformation technique called root transformation. The efficacy of the proposed technique is assessed by conducting a simulation study using gamma, Weibull, and beta distributions. The root transformation technique is used to estimate the PCI for each set of simulated data. These results are then compared with the PCI obtained using exact percentiles and the Box-Cox method. Finally, a case study based on real-world data is presented.

Enzyme and Microbial Technology, 2002

D-Xylulokinase (ATP: D-xylulose 5-phosphotransferase EC 2.7.1.17) was purified from a newly isola... more D-Xylulokinase (ATP: D-xylulose 5-phosphotransferase EC 2.7.1.17) was purified from a newly isolated thermophilic Saccharococcus caldoxylosilyticus in which the enzyme is constitutively expressed. The purified enzyme had a specific activity of 60 U/mg at 25°C, and 185 U/mg in its optimum temperature range of between 65 and 75°C. Its K m for xylulose was 0.09 mM at 25°C, and for MgATP 0.16 mM. The molecular mass of the monomer was estimated to be 54 kDa, the holoenzyme comprising two subunits. Stability studies showed that the enzyme was stable up to 65°C, but denatured rapidly at 75°C in Tris buffer. However, it was stabilised by xylulose, which accounts for its high optimum temperature for activity. N-terminal amino acid analysis produced the sequence DHVIGVDLGTSAVKALLVD . . . which has 65% identity with two other Bacillus xylulokinases as deduced from their gene sequences, and somewhat less identity with other known xylulokinase sequences.

Several closely related, xylanolytic, thermophilic bacilli were isolated from local soils on xylo... more Several closely related, xylanolytic, thermophilic bacilli were isolated from local soils on xylose-containing minimal medium. On the basis of morphology and biochemical characteristics, one of the isolates, designated strain S1812 T (T l type strain), was studied further. Strain S1812 T was a xylanolytic, sporulating, Gram-positive, rod-shaped bacterium. Its Gram-positive nature was confirmed by electron microscopic examination of thin sections of the cells. The isolate was a thermophilic (optimum temperature for growth, 65 SC), facultative anaerobe that grew on a wide range of carbon sources including glucose, lactose, starch and xylose. It expressed high levels of both xylose isomerase and xylulokinase on xylose and also on glucose. The DNA GMC content was 44 mol %. rRNA gene sequence analysis placed strain S1812 T in Bacillus cluster 5 ; it was more closely related to Saccharococcus thermophilus than to thermophilic Bacillus species. DNA-DNA hybridization also indicated its close relationship to S. thermophilus. Based on the evidence presented, it is proposed that strain S1812 T be designated Saccharococcus caldoxylosilyticus sp. nov. Strain S1812 T is the type strain (l ATCC 700356 T l DSM 97-987 T ).

Nuovo Cimento Della Societa Italiana Di Fisica A-nuclei Particles and Fields, 1990

In the present paper a study of the interactions caused by 340 GeV negative pions with emulsion n... more In the present paper a study of the interactions caused by 340 GeV negative pions with emulsion nuclei has been carried out. Two-particle rapidity-gap correlation gives an evidence that the particle production takes place via cluster formation. From the study of short-short and long-short correlation, it is observed that a cluster should consist of at least three charged particles. Cluster size has also been investigated. The production of heavy clusters is found to be energy dependent.

Physica Scripta, 1981

Production of deuterons in 24 GeV/c proton and 50 GeV/c pion interactions with emulsion nuclei ha... more Production of deuterons in 24 GeV/c proton and 50 GeV/c pion interactions with emulsion nuclei has been investigated. Some characteristics of stars in which deuterons have been observed have been compared with the average characteristics of stars. It has been found that (i) for any given value of ng the average excitation of deuteron producing stars is higher than the total sample and (ii) the average shower multiplicity in stars with less energetic deuterons is higher than of the events with energetic deuterons or of the ordinary sample. None of the existing models for deuteron production seems to be capable of explaining the observed features.

Nuclear Physics B, 1985

Experimental results on ,r--emulsion interactions at 340 GeV/c are presented. The dependence of R... more Experimental results on ,r--emulsion interactions at 340 GeV/c are presented. The dependence of R on the target mass is studied in the light of constituent quark models. A universal relation for the (N~) dependence on (Nch) and (VA) is obtained. Systematics of shower multiplicity distributions are also studied and a new scaling function for integral probability distributions of shower tracks is worked out.

Nuovo Cimento Della Societa Italiana Di Fisica A-nuclei Particles and Fields, 1994

... [6] M. TARIQ, M. ZAFAR, A. TUFAIL and S. AHMAD: submitted to Int. J. Mod. Phys. E. [7] A. EL-... more ... [6] M. TARIQ, M. ZAFAR, A. TUFAIL and S. AHMAD: submitted to Int. J. Mod. Phys. E. [7] A. EL-NAGHY: Nuovo Cimento A, 71, 245 (1982) and references therein. [8] T. AHMAD, M. TARIQ,M. IRFAN, M. ZhFAR, MZ AHSAN and M. SHAFI: Can. J. Phys., 67, 519 (1989).

Physica Scripta, 1983

In the present work we report some results on multiparticle production in 50 GeV/c π--interaction... more In the present work we report some results on multiparticle production in 50 GeV/c π--interactions with emulsion nuclei. The general characteristics of heavy and shower particle multiplicity distributions are compared with the results from p-nucleus collisions at the same incident energy. The various experimental results have also been compared with the predictions of the existing theoretical models. We have observed that the mean normalized multiplicity (RA2) in hadron-nucleus interactions as a function of the effective number of projectile encounters, langleν'rangle, calculated by using the additive quark model suggests a new kind of scaling and RA2 vs. langleν'rangle is independent of nature of the projectile.

Physical Review D, 1990

... 4) 4 27 1990 The American Physical Society PHYSICAL REVIEW D I OCTOBER 1990 42 2187 A. TUFAIL... more ... 4) 4 27 1990 The American Physical Society PHYSICAL REVIEW D I OCTOBER 1990 42 2187 A. TUFAIL, S. AHMAD, AR KHAN, M. ZAFAR ... Spectator quarks are absorbed in nuclear matter with an absorption cross sec-tion: a inel 10a inel ~~~~~13) aqN =(/n)hN ,(3 where a ...