1,127 research outputs found
Conformal Collineations and Ricci Inheritance Symmetry in String Cloud and String Fluids
Conformal collineations (a generalization of conformal motion) and Ricci
inheritance collineations, defined by , for
string cloud and string fluids in general relativity are studied. By
investigating the kinematical and dynamical properties of such fluids and using
the field equations, some recent studies on the restrictions imposed by
conformal collineations are extended, and new results are found.Comment: 12 pages, LaTeX, no figures, to appear in Int. J. Mod. Phys.
Lightlike Submanifolds of Indefinite Sasakian Manifolds
We first prove some results on invariant lightlike
submanifolds of indefinite Sasakian manifolds. Then, we introduce a general notion of contact Cauchy-Riemann (CR) lightlike submanifolds and study the geometry of leaves of their distributions. We also study a class, namely, contact screen Cauchy-Riemann (SCR) lightlike submanifolds which include invariant and screen real subcases. Finally, we prove characterization theorems on the existence of contact SCR, screen real, invariant, and contact CR minimal lightlike submanifolds
Hypersurfaces in a conformally flat space with curvature collineation
We classify the shape operators of Einstein and pseudo Einstein hypersurfaces in a
conformally flat space with a symmetry called curvature collineation. We solve the fundamental
problem of finding all possible forms of non-diagonalizable shape operators. A physical example
of space-time with matter is presented to show that the energy condition has direct relation with
the diagonalizability of shape operator
Conformal Ricci collineations of static spherically symmetric spacetimes
Conformal Ricci collineations of static spherically symmetric spacetimes are
studied. The general form of the vector fields generating conformal Ricci
collineations is found when the Ricci tensor is non-degenerate, in which case
the number of independent conformal Ricci collineations is \emph{fifteen}; the
maximum number for 4-dimensional manifolds. In the degenerate case it is found
that the static spherically symmetric spacetimes always have an infinite number
of conformal Ricci collineations. Some examples are provided which admit
non-trivial conformal Ricci collineations, and perfect fluid source of the
matter
Spacelike Ricci Inheritance Vectors in a Model of String Cloud and String Fluid Stress Tensor
We study the consequences of the existence of spacelike Ricci inheritance
vectors (SpRIVs) parallel to for model of string cloud and string fluid
stress tensor in the context of general relativity. Necessary and sufficient
conditions are derived for a spacetime with a model of string cloud and string
fluid stress tensor to admit a SpRIV and a SpRIV which is also a spacelike
conformal Killing vector (SpCKV). Also, some results are obtained.Comment: 11 page
Ricci Collineations for type B warped space-times
We present the general structure of proper Ricci Collineations (RC) for type
B warped space-times. Within this framework, we give a detailed description of
the most general proper RC for spherically symmetric metrics. As examples,
static spherically symmetric and Friedmann-Robertson-Walker space-times are
considered.Comment: 18 pages, Latex, To appear in GR
On global models for isolated rotating axisymmetric charged bodies; uniqueness of the exterior field
A relatively recent study by Mars and Senovilla provided us with a uniqueness
result for the exterior vacuum gravitational field generated by an isolated
distribution of matter in axial rotation in equilibrium in General Relativity.
The generalisation to exterior electrovacuum gravitational fields, to include
charged rotating objects, is presented here.Comment: LaTeX, 21 pages, uses iopart styl
Unbiased Metagenomic Sequencing for Pediatric Meningitis in Bangladesh Reveals Neuroinvasive Chikungunya Virus Outbreak and Other Unrealized Pathogens.
The burden of meningitis in low-and-middle-income countries remains significant, but the infectious causes remain largely unknown, impeding institution of evidence-based treatment and prevention decisions. We conducted a validation and application study of unbiased metagenomic next-generation sequencing (mNGS) to elucidate etiologies of meningitis in Bangladesh. This RNA mNGS study was performed on cerebrospinal fluid (CSF) specimens from patients admitted in the largest pediatric hospital, a World Health Organization sentinel site, with known neurologic infections (n = 36), with idiopathic meningitis (n = 25), and with no infection (n = 30), and six environmental samples, collected between 2012 and 2018. We used the IDseq bioinformatics pipeline and machine learning to identify potentially pathogenic microbes, which we then confirmed orthogonally and followed up through phone/home visits. In samples with known etiology and without infections, there was 83% concordance between mNGS and conventional testing. In idiopathic cases, mNGS identified a potential bacterial or viral etiology in 40%. There were three instances of neuroinvasive Chikungunya virus (CHIKV), whose genomes were >99% identical to each other and to a Bangladeshi strain only previously recognized to cause febrile illness in 2017. CHIKV-specific qPCR of all remaining stored CSF samples from children who presented with idiopathic meningitis in 2017 (n = 472) revealed 17 additional CHIKV meningitis cases, exposing an unrecognized meningitis outbreak. Orthogonal molecular confirmation, case-based clinical data, and patient follow-up substantiated the findings. Case-control CSF mNGS surveys can complement conventional diagnostic methods to identify etiologies of meningitis, conduct surveillance, and predict outbreaks. The improved patient- and population-level data can inform evidence-based policy decisions.IMPORTANCE Globally, there are an estimated 10.6 million cases of meningitis and 288,000 deaths every year, with the vast majority occurring in low- and middle-income countries. In addition, many survivors suffer from long-term neurological sequelae. Most laboratories assay only for common bacterial etiologies using culture and directed PCR, and the majority of meningitis cases lack microbiological diagnoses, impeding institution of evidence-based treatment and prevention strategies. We report here the results of a validation and application study of using unbiased metagenomic sequencing to determine etiologies of idiopathic (of unknown cause) cases. This included CSF from patients with known neurologic infections, with idiopathic meningitis, and without infection admitted in the largest children's hospital of Bangladesh and environmental samples. Using mNGS and machine learning, we identified and confirmed an etiology (viral or bacterial) in 40% of idiopathic cases. We detected three instances of Chikungunya virus (CHIKV) that were >99% identical to each other and to a strain previously recognized to cause systemic illness only in 2017. CHIKV qPCR of all remaining stored 472 CSF samples from children who presented with idiopathic meningitis in 2017 at the same hospital uncovered an unrecognized CHIKV meningitis outbreak. CSF mNGS can complement conventional diagnostic methods to identify etiologies of meningitis, and the improved patient- and population-level data can inform better policy decisions
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