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

Papers by Faiz Ahmad

Frequency shifts in a single-mode laser

Journal of Physics A: Mathematical, Nuclear and General, 1974

The semi-classical laser equations are analysed outside the rotating-wave approximation and a new... more The semi-classical laser equations are analysed outside the rotating-wave approximation and a new exact steady-state solution for stationary but inhomogeneously broadened atoms is obtained. Results applicable to any solid-state laser are derived and these are also relevant to a gas laser working near threshold or at very high intensities. The resonance frequency exhibits a Bloch-Siegert shift. New results in the

Neurosurgery, Jan 29, 2017

Cranioplasty after decompressive craniectomy (DC) is routinely performed for reconstructive purpo... more Cranioplasty after decompressive craniectomy (DC) is routinely performed for reconstructive purposes and has been recently linked to improved cerebral blood flow (CBF) and neurological function. To systematically review all available literature to evaluate the effect of cranioplasty on CBF and neurocognitive recovery. A PubMed, Google Scholar, and MEDLINE search adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines included studies reporting patients who underwent DC and subsequent cranioplasty in whom cerebral hemodynamics were measured before and after cranioplasty. The search yielded 21 articles with a total of 205 patients (range 3-76 years) who underwent DC and subsequent cranioplasty. Two studies enrolled 29 control subjects for a total of 234 subjects. Studies used different imaging modalities, including CT perfusion (n = 10), Xenon-CT (n = 3), single-photon emission CT (n = 2), transcranial Doppler (n = 6), MR perfusion (n = 1), and positr...

Double cervical fracture-subluxation at adjacent levels

The Spine Journal, 2016

Neurosurgical focus, 2015

OBJECT The craniovertebral junction (CVJ) is unique in the spinal column regarding the degree of ... more OBJECT The craniovertebral junction (CVJ) is unique in the spinal column regarding the degree of multiplanar mobility allowed by its bony articulations. A network of ligamentous attachments provides stability to this junction. Although ligamentous injury can be inferred on CT scans through the utilization of craniometric measurements, the disruption of these ligaments can only be visualized directly with MRI. Here, the authors review the current literature on MRI evaluation of the CVJ following trauma and present several illustrative cases to highlight the utility and limitations of craniometric measures in the context of ligamentous injury at the CVJ. METHODS A retrospective case review was conducted to identify patients with cervical spine trauma who underwent cervical MRI and subsequently required occipitocervical or atlantoaxial fusion. Craniometric measurements were performed on the CT images in these cases. An extensive PubMed/MEDLINE literature search was conducted to identif...

Anterior Thigh Compartment Syndrome and Local Myonecrosis After Posterior Spine Surgery on a Jackson Table

World Neurosurgery, 2012

Acute compartment syndrome (ACS) after posterior spinal surgery is very uncommon. Most of the rep... more Acute compartment syndrome (ACS) after posterior spinal surgery is very uncommon. Most of the reported cases have ACS in the legs related to positioning in the knee-chest position; postoperative ACS in the thighs is exceedingly rare, with only one reported case (17). This study reports two patients who had local muscle necrosis/ACS after spine surgery in the prone position and discusses preventive measures. Both of our complications were probably related to reversing the position of the iliac crest and hip pads on a Jackson operating table, which was done to achieve better lumbar lordosis. Our cases indicate the need for a high index of suspicion of ACS in patients who have persistent unresolved pain and local swelling. Tissue pressure monitoring is an option in suspected cases. Iliac crest and thigh pads should not be reversed during positioning on a Jackson table.

Management of Nerve Sheath Tumors Involving the Spine

Schmidek and Sweet Operative Neurosurgical Techniques, 2012

TAG Theoretical and Applied Genetics, 1999

Localization and activity of rRNA genes on fenugreek (Trigonella foenum-graecum L.) chromosomes b... more Localization and activity of rRNA genes on fenugreek (Trigonella foenum-graecum L.) chromosomes by fluorescent in situ hybridization and silver staining

Cerebellopontine angle meningeal melanocytoma: a rare tumor in an uncommon location

Journal of Neurosurgery, 2007

✓Meningeal melanocytomas are uncommon intracranial tumors and their occurrence at the cerebellopo... more ✓Meningeal melanocytomas are uncommon intracranial tumors and their occurrence at the cerebellopontine angle (CPA) is extremely rare. The authors describe the case of a 58-year-old woman who presented with a left CPA tumor; on the basis of histopathological studies after resection, a diagnosis of meningeal melanocytoma was reached. The relevant literature is reviewed.

Journal of Applied Sciences, 2012

Linear Invariants of a Cartesian Tensor Under SO(2), SO(3) and SO(4)

International Journal of Theoretical Physics, 2010

Abstract A general theory for finding the invariants of an arbitrary tensor is described. Group t... more Abstract A general theory for finding the invariants of an arbitrary tensor is described. Group theoretic methods produce formulas which precisely determine the number of invariants for a Cartesian tensor of arbitrary rank defined over a space of dimension 2, 3 or 4. Explicit ...

Injection molding of SiC-reinforced PM aluminum matrix composites

International journal of powder metallurgy, 2006

Résumé/Abstract Optimum machine molding parameters were identified and defect-free moldings of Si... more Résumé/Abstract Optimum machine molding parameters were identified and defect-free moldings of SiC-reinforced aluminum alloy matrix composites (AMCs) were produced by powder injection molding (PIM). Fiber orientation was characterized qualitatively. Highly ...

Communications in Nonlinear Science and Numerical Simulation, 2009

The [4/3] Pade approximant for the derivative is modified so that the resulting expression has th... more The [4/3] Pade approximant for the derivative is modified so that the resulting expression has the required asymptotic behavior. This gives an analytical result which represents the solution of the classical Blasius problem on the whole domain.

Gross total excision of pediatric giant cystic craniopharyngioma with huge retroclival extension to the level of foramen magnum by anterior trans petrous approach: report of two cases and review of literature

Child's Nervous System, 2007

Craniopharyngiomas with a large posterior fossa extension beyond the level of the foramen magnum ... more Craniopharyngiomas with a large posterior fossa extension beyond the level of the foramen magnum are very rare and usually removed in two stages. The objective of this paper is to report that such rare cases of giant cystic predominantly retrochiasmatic retroclival craniopharyngiomas can be completely excised by an anterior transpetrous approach in a single stage. The first case was a 6-year-old boy who presented with a 1-year history of recurrent episodes of seizures, headache, and vomiting. The second case was a 10-year-old girl who presented with history of headache, visual deterioration, and left-side hemiparesis for one and half years. Preoperative computed tomography (CT) and magnetic resonance imaging (MRI) in both these patients revealed a giant sellar suprasellar cystic lesion with areas of calcification and the lesion was predominantly retrochiasmatic with a huge retroclival posterior fossa extension down to the level of the C1 vertebra and laterally to the cerebellopontine angle. Gross total excision of both suprasellar and posterior fossa extensions could be done in both the patients through an anterior transpetrous transtentorial approach (Kawase's approach). Postoperative imaging (MRI/CT) revealed no obvious evidence of residual tumor. The first patient had right hemiparesis from which he recovered completely. The second patient died suddenly on postoperative day 4 after initial uneventful postoperative period, and the exact cause of death is not known. Giant cystic craniopharyngiomas, which are predominantly retrochiasmatic and associated with huge retroclival posterior fossa extensions, can be removed in single stage by Kawase's approach.

Annals of Indian Academy of Neurology, 2016

hemorrhagic stroke have higher short-term mortality, but ischemic stroke patients have a signific... more hemorrhagic stroke have higher short-term mortality, but ischemic stroke patients have a significant long-term disability and morbidity. Long-term rehabilitation of stroke survivors includesmultidisciplinary care looking at neurological, physical, social, and emotional aspects. Endocrine disorders contribute to the long-term morbidity of the stroke survivors and are often undiagnosed due to lack of significant symptoms attributable to the hormonal dysfunction. Endocrine disorders are reported to occur in 15-55% of stroke survivors. The blood supply of pituitary and hypothalamus affects during the vascular compromise in the brain. The most common endocrine disorders include alterations in thyroid and gonadal axes. Previous reportsshowed the ability of the hormonal parameters in the prediction of long-term disability. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) administration resulted in the neuroprotective effects in animal and human studies. There is no significant research on the endocrine disabilities inthe acute phase of stroke and also about the endocrine dysfunction with respect to the etiology of CVA. Hence, we conducted this study to assess the prevalence of occult endocrine dysfunction in patients of stroke during the

A review on nanowires as an alternative high density magnetic storage media

ABSTRACT The thirst to design high density magnetic storage media with improved efficiency has al... more ABSTRACT The thirst to design high density magnetic storage media with improved efficiency has always been one of the basic challenges in computer industry. In this paper, present challenges of magnetic storage media and different parameters that can affect the properties of magnetic nanowires have been investigated in detail. The magnetic nanowires are the promising candidate for the future high density magnetic storage media. So far the grain isolation is a problem while using thin film magnetic storage media. Further, during miniaturization, superparamagnetic limit is reached due to increasing thermal effects at this scale which makes the magnetic grains of magnetic nanowires susceptible to thermal fluctuations. To overcome this problem of superparamagnetism and grain isolation, nanowires with high coercivity, remanent magnetization and thermal stability are thought to be the alternatives. Alloy and multilayered magnetic nanowires prepared by some less expensive technique with suitable magnetic and thermal properties can serve to overcome this challenge.

International Journal of Applied Physics and Mathematics, 2011

In this study, the flow behavior of multi-walled carbon nanotubes (CNTs) reinforced copper matrix... more In this study, the flow behavior of multi-walled carbon nanotubes (CNTs) reinforced copper matrix feedstocks is presented. The solid loadings in the copper feedstock were investigated in the ranges of 55-61 Vol. % using binder. Pure copper (Cu) and Cu/CNTs feedstocks were compounded using internal mixer machine for homogenous dispersion of solids in the binder. The flow behavior was measured using a capillary rheometer in the shear rate range expected to occur during powder injection molding. An acceptable increasing trend in viscosity of the copper feedstock with powder loading was recorded. Cu/CNTs composite feedstocks showed viscosity more than 1000 Pa.s which is most probably due to the addition of CNTs and increasing trend in viscosity of Cu/CNTs was noted as well. The results also identified that the feedstock containing 59 vol. % copper was most suitable for substitution of CNTs in Cu feedstock.

The Quarterly Journal of Mechanics and Applied Mathematics, 2008

The number of linear invariants under SO(3) as well as SO(2) of a Cartesian tensor of an arbitrar... more The number of linear invariants under SO(3) as well as SO(2) of a Cartesian tensor of an arbitrary rank is studied. A linear form is defined in terms of elements of a tensor. It is established that the number of linear invariants of a tensor of rank n under SO(3) equals the dimension of the space of isotropic tensors of rank n. Formulas for the number of invariants in the two cases are also derived. For the elasticity tensor, our analysis confirms the results of Norris.

Endoscopic excision of intraventricular neurocysticercosis in children: a series of six cases and review

Child's Nervous System, 2007

Neurocysticercosis (NCC) affects both adults and children, but it is uncommon in childhood. The c... more Neurocysticercosis (NCC) affects both adults and children, but it is uncommon in childhood. The clinical presentation and management of intraventricular neurocysticercosis (IVNCC) in children has not been described adequately. We, therefore, present our series of six children with IVNCC managed by endoscopic excision. A retrospective analysis of six children with IVNCC was performed. The endoscopic technique practiced is described. Complete excision of the intraventricular cyst was performed in all patients. Simultaneously, five endoscopic third ventriculostomies, one septostomy, and one foramenotomy were performed. There were no perioperative and postoperative complications. Mean follow-up duration was 24.8 months. Clinical improvement was seen in all children, and none required shunting. Follow-up radiology showed no residual lesion and decreased ventricle size in all patients. Endoscopic IVNCC cyst excision along with internal CSF diversion is a safe and effective option and avoids shunt and its related complications in these children.

Frequency shifts in a single-mode laser

Journal of Physics A: Mathematical, Nuclear and General, 1974

The semi-classical laser equations are analysed outside the rotating-wave approximation and a new... more The semi-classical laser equations are analysed outside the rotating-wave approximation and a new exact steady-state solution for stationary but inhomogeneously broadened atoms is obtained. Results applicable to any solid-state laser are derived and these are also relevant to a gas laser working near threshold or at very high intensities. The resonance frequency exhibits a Bloch-Siegert shift. New results in the

Neurosurgery, Jan 29, 2017

Cranioplasty after decompressive craniectomy (DC) is routinely performed for reconstructive purpo... more Cranioplasty after decompressive craniectomy (DC) is routinely performed for reconstructive purposes and has been recently linked to improved cerebral blood flow (CBF) and neurological function. To systematically review all available literature to evaluate the effect of cranioplasty on CBF and neurocognitive recovery. A PubMed, Google Scholar, and MEDLINE search adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines included studies reporting patients who underwent DC and subsequent cranioplasty in whom cerebral hemodynamics were measured before and after cranioplasty. The search yielded 21 articles with a total of 205 patients (range 3-76 years) who underwent DC and subsequent cranioplasty. Two studies enrolled 29 control subjects for a total of 234 subjects. Studies used different imaging modalities, including CT perfusion (n = 10), Xenon-CT (n = 3), single-photon emission CT (n = 2), transcranial Doppler (n = 6), MR perfusion (n = 1), and positr...

Double cervical fracture-subluxation at adjacent levels

The Spine Journal, 2016

Neurosurgical focus, 2015

OBJECT The craniovertebral junction (CVJ) is unique in the spinal column regarding the degree of ... more OBJECT The craniovertebral junction (CVJ) is unique in the spinal column regarding the degree of multiplanar mobility allowed by its bony articulations. A network of ligamentous attachments provides stability to this junction. Although ligamentous injury can be inferred on CT scans through the utilization of craniometric measurements, the disruption of these ligaments can only be visualized directly with MRI. Here, the authors review the current literature on MRI evaluation of the CVJ following trauma and present several illustrative cases to highlight the utility and limitations of craniometric measures in the context of ligamentous injury at the CVJ. METHODS A retrospective case review was conducted to identify patients with cervical spine trauma who underwent cervical MRI and subsequently required occipitocervical or atlantoaxial fusion. Craniometric measurements were performed on the CT images in these cases. An extensive PubMed/MEDLINE literature search was conducted to identif...

Anterior Thigh Compartment Syndrome and Local Myonecrosis After Posterior Spine Surgery on a Jackson Table

World Neurosurgery, 2012

Acute compartment syndrome (ACS) after posterior spinal surgery is very uncommon. Most of the rep... more Acute compartment syndrome (ACS) after posterior spinal surgery is very uncommon. Most of the reported cases have ACS in the legs related to positioning in the knee-chest position; postoperative ACS in the thighs is exceedingly rare, with only one reported case (17). This study reports two patients who had local muscle necrosis/ACS after spine surgery in the prone position and discusses preventive measures. Both of our complications were probably related to reversing the position of the iliac crest and hip pads on a Jackson operating table, which was done to achieve better lumbar lordosis. Our cases indicate the need for a high index of suspicion of ACS in patients who have persistent unresolved pain and local swelling. Tissue pressure monitoring is an option in suspected cases. Iliac crest and thigh pads should not be reversed during positioning on a Jackson table.

Management of Nerve Sheath Tumors Involving the Spine

Schmidek and Sweet Operative Neurosurgical Techniques, 2012

TAG Theoretical and Applied Genetics, 1999

Localization and activity of rRNA genes on fenugreek (Trigonella foenum-graecum L.) chromosomes b... more Localization and activity of rRNA genes on fenugreek (Trigonella foenum-graecum L.) chromosomes by fluorescent in situ hybridization and silver staining

Cerebellopontine angle meningeal melanocytoma: a rare tumor in an uncommon location

Journal of Neurosurgery, 2007

✓Meningeal melanocytomas are uncommon intracranial tumors and their occurrence at the cerebellopo... more ✓Meningeal melanocytomas are uncommon intracranial tumors and their occurrence at the cerebellopontine angle (CPA) is extremely rare. The authors describe the case of a 58-year-old woman who presented with a left CPA tumor; on the basis of histopathological studies after resection, a diagnosis of meningeal melanocytoma was reached. The relevant literature is reviewed.

Journal of Applied Sciences, 2012

Linear Invariants of a Cartesian Tensor Under SO(2), SO(3) and SO(4)

International Journal of Theoretical Physics, 2010

Abstract A general theory for finding the invariants of an arbitrary tensor is described. Group t... more Abstract A general theory for finding the invariants of an arbitrary tensor is described. Group theoretic methods produce formulas which precisely determine the number of invariants for a Cartesian tensor of arbitrary rank defined over a space of dimension 2, 3 or 4. Explicit ...

Injection molding of SiC-reinforced PM aluminum matrix composites

International journal of powder metallurgy, 2006

Résumé/Abstract Optimum machine molding parameters were identified and defect-free moldings of Si... more Résumé/Abstract Optimum machine molding parameters were identified and defect-free moldings of SiC-reinforced aluminum alloy matrix composites (AMCs) were produced by powder injection molding (PIM). Fiber orientation was characterized qualitatively. Highly ...

Communications in Nonlinear Science and Numerical Simulation, 2009

The [4/3] Pade approximant for the derivative is modified so that the resulting expression has th... more The [4/3] Pade approximant for the derivative is modified so that the resulting expression has the required asymptotic behavior. This gives an analytical result which represents the solution of the classical Blasius problem on the whole domain.

Gross total excision of pediatric giant cystic craniopharyngioma with huge retroclival extension to the level of foramen magnum by anterior trans petrous approach: report of two cases and review of literature

Child's Nervous System, 2007

Craniopharyngiomas with a large posterior fossa extension beyond the level of the foramen magnum ... more Craniopharyngiomas with a large posterior fossa extension beyond the level of the foramen magnum are very rare and usually removed in two stages. The objective of this paper is to report that such rare cases of giant cystic predominantly retrochiasmatic retroclival craniopharyngiomas can be completely excised by an anterior transpetrous approach in a single stage. The first case was a 6-year-old boy who presented with a 1-year history of recurrent episodes of seizures, headache, and vomiting. The second case was a 10-year-old girl who presented with history of headache, visual deterioration, and left-side hemiparesis for one and half years. Preoperative computed tomography (CT) and magnetic resonance imaging (MRI) in both these patients revealed a giant sellar suprasellar cystic lesion with areas of calcification and the lesion was predominantly retrochiasmatic with a huge retroclival posterior fossa extension down to the level of the C1 vertebra and laterally to the cerebellopontine angle. Gross total excision of both suprasellar and posterior fossa extensions could be done in both the patients through an anterior transpetrous transtentorial approach (Kawase's approach). Postoperative imaging (MRI/CT) revealed no obvious evidence of residual tumor. The first patient had right hemiparesis from which he recovered completely. The second patient died suddenly on postoperative day 4 after initial uneventful postoperative period, and the exact cause of death is not known. Giant cystic craniopharyngiomas, which are predominantly retrochiasmatic and associated with huge retroclival posterior fossa extensions, can be removed in single stage by Kawase's approach.

Annals of Indian Academy of Neurology, 2016

hemorrhagic stroke have higher short-term mortality, but ischemic stroke patients have a signific... more hemorrhagic stroke have higher short-term mortality, but ischemic stroke patients have a significant long-term disability and morbidity. Long-term rehabilitation of stroke survivors includesmultidisciplinary care looking at neurological, physical, social, and emotional aspects. Endocrine disorders contribute to the long-term morbidity of the stroke survivors and are often undiagnosed due to lack of significant symptoms attributable to the hormonal dysfunction. Endocrine disorders are reported to occur in 15-55% of stroke survivors. The blood supply of pituitary and hypothalamus affects during the vascular compromise in the brain. The most common endocrine disorders include alterations in thyroid and gonadal axes. Previous reportsshowed the ability of the hormonal parameters in the prediction of long-term disability. Growth hormone (GH) and insulin-like growth factor-1 (IGF-1) administration resulted in the neuroprotective effects in animal and human studies. There is no significant research on the endocrine disabilities inthe acute phase of stroke and also about the endocrine dysfunction with respect to the etiology of CVA. Hence, we conducted this study to assess the prevalence of occult endocrine dysfunction in patients of stroke during the

A review on nanowires as an alternative high density magnetic storage media

ABSTRACT The thirst to design high density magnetic storage media with improved efficiency has al... more ABSTRACT The thirst to design high density magnetic storage media with improved efficiency has always been one of the basic challenges in computer industry. In this paper, present challenges of magnetic storage media and different parameters that can affect the properties of magnetic nanowires have been investigated in detail. The magnetic nanowires are the promising candidate for the future high density magnetic storage media. So far the grain isolation is a problem while using thin film magnetic storage media. Further, during miniaturization, superparamagnetic limit is reached due to increasing thermal effects at this scale which makes the magnetic grains of magnetic nanowires susceptible to thermal fluctuations. To overcome this problem of superparamagnetism and grain isolation, nanowires with high coercivity, remanent magnetization and thermal stability are thought to be the alternatives. Alloy and multilayered magnetic nanowires prepared by some less expensive technique with suitable magnetic and thermal properties can serve to overcome this challenge.

International Journal of Applied Physics and Mathematics, 2011

In this study, the flow behavior of multi-walled carbon nanotubes (CNTs) reinforced copper matrix... more In this study, the flow behavior of multi-walled carbon nanotubes (CNTs) reinforced copper matrix feedstocks is presented. The solid loadings in the copper feedstock were investigated in the ranges of 55-61 Vol. % using binder. Pure copper (Cu) and Cu/CNTs feedstocks were compounded using internal mixer machine for homogenous dispersion of solids in the binder. The flow behavior was measured using a capillary rheometer in the shear rate range expected to occur during powder injection molding. An acceptable increasing trend in viscosity of the copper feedstock with powder loading was recorded. Cu/CNTs composite feedstocks showed viscosity more than 1000 Pa.s which is most probably due to the addition of CNTs and increasing trend in viscosity of Cu/CNTs was noted as well. The results also identified that the feedstock containing 59 vol. % copper was most suitable for substitution of CNTs in Cu feedstock.

The Quarterly Journal of Mechanics and Applied Mathematics, 2008

The number of linear invariants under SO(3) as well as SO(2) of a Cartesian tensor of an arbitrar... more The number of linear invariants under SO(3) as well as SO(2) of a Cartesian tensor of an arbitrary rank is studied. A linear form is defined in terms of elements of a tensor. It is established that the number of linear invariants of a tensor of rank n under SO(3) equals the dimension of the space of isotropic tensors of rank n. Formulas for the number of invariants in the two cases are also derived. For the elasticity tensor, our analysis confirms the results of Norris.

Endoscopic excision of intraventricular neurocysticercosis in children: a series of six cases and review

Child's Nervous System, 2007

Neurocysticercosis (NCC) affects both adults and children, but it is uncommon in childhood. The c... more Neurocysticercosis (NCC) affects both adults and children, but it is uncommon in childhood. The clinical presentation and management of intraventricular neurocysticercosis (IVNCC) in children has not been described adequately. We, therefore, present our series of six children with IVNCC managed by endoscopic excision. A retrospective analysis of six children with IVNCC was performed. The endoscopic technique practiced is described. Complete excision of the intraventricular cyst was performed in all patients. Simultaneously, five endoscopic third ventriculostomies, one septostomy, and one foramenotomy were performed. There were no perioperative and postoperative complications. Mean follow-up duration was 24.8 months. Clinical improvement was seen in all children, and none required shunting. Follow-up radiology showed no residual lesion and decreased ventricle size in all patients. Endoscopic IVNCC cyst excision along with internal CSF diversion is a safe and effective option and avoids shunt and its related complications in these children.