We model massive dark objects in galactic nuclei as spherically symmetric static naked singularities in the Einstein massless scalar field theory and study the resulting gravitational lensing in detail. Based on whether or not a naked singularity is covered within a photon sphere we classify naked singularities into two kinds: weakly naked (those contained within at least one photon sphere) and strongly naked (those not contained within any photon sphere). The qualitative features of gravitational lensing due to a weakly naked singularity are similar to those due to a Schwarzschild black hole (these give rise to one Einstein ring but no radial critical curve). However, the gravitational lensing due to a strongly naked singularity is qualitatively different from that due to a Schwarzschild black hole; a strongly naked singularity gives rise to either two or nil Einstein ring(s) and one radial critical curve. A light ray passing close to a photon sphere of a black hole or a weakly naked singularity goes around its photon sphere once, twice, or many times (before reaching an observer) depending upon the impact parameter and thus gives rise to a sequence of theoretically infinite number of relativistic images, which are highly demagnified. A strongly naked singularity produces no relativistic images.
The mouse-sized naked mole rat (Heterocephalus glaber) is a very unusual mammal. It is a social animal, living in groups in burrows beneath arid African deserts. It can live for 30 or more years in atmospheres with low oxygen and high carbon dioxide, and is remarkably resistant to cancer. So the genome sequence, published in this issue, might be expected to contain some intriguing characteristics. Analysis of the genome and its transcriptome reveals unusual genomic features and molecular adaptations including strategies for improved genome stability, low mutation rate and improved protein maintenance. The data also reveal molecular adaptations consistent with poor visual function, poikilothermy, hairlessness, circadian rhythms, taste sensing and insensitivity to low oxygen. The naked mole rat (Heterocephalus glaber) is a strictly subterranean, extraordinarily long-lived eusocial mammal1. Although it is the size of a mouse, its maximum lifespan exceeds 30 years, making this animal the longest-living rodent. Naked mole rats show negligible senescence, no age-related increase in mortality, and high fecundity until death2. In addition to delayed ageing, they are resistant to both spontaneous cancer and experimentally induced tumorigenesis3,4. Naked mole rats pose a challenge to the theories that link ageing, cancer and redox homeostasis. Although characterized by significant oxidative stress5, the naked mole rat proteome does not show age-related susceptibility to oxidative damage or increased ubiquitination6. Naked mole rats naturally reside in large colonies with a single breeding female, the ‘queen’, who suppresses the sexual maturity of her subordinates7. They also live in full darkness, at low oxygen and high carbon dioxide concentrations8, and are unable to sustain thermogenesis9 nor feel certain types of pain10,11. Here we report the sequencing and analysis of the naked mole rat genome, which reveals unique genome features and molecular adaptations consistent with cancer resistance, poikilothermy, hairlessness and insensitivity to low oxygen, and altered visual function, circadian rythms and taste sensing. This information provides insights into the naked mole rat’s exceptional longevity and ability to live in hostile conditions, in the dark and at low oxygen. The extreme traits of the naked mole rat, together with the reported genome and transcriptome information, offer opportunities for understanding ageing and advancing other areas of biological and biomedical research.
We model the massive dark object at the center of the Galaxy as a Schwarzschild black hole as well as Janis-Newman-Winicour naked singularities, characterized by the mass and scalar charge parameters, and study gravitational lensing (particularly time delay, magnification centroid, and total magnification) by them. We find that the lensing features are qualitatively similar (though quantitatively different) for Schwarzschild black holes, weakly naked, and marginally strongly naked singularities. However, the lensing characteristics of strongly naked singularities are qualitatively very different from those due to Schwarzschild black holes. The images produced by Schwarzschild black hole lenses and weakly naked and marginally strongly naked singularity lenses always have positive time delays. On the other hand, strongly naked singularity lenses can give rise to images with positive, zero, or negative time delays. In particular, for a large angular source position the direct image (the outermost image on the same side as the source) due to strongly naked singularity lensing always has a negative time delay. We also found that the scalar field decreases the time delay and increases the total magnification of images; this result could have important implications for cosmology. As the Janis-Newman-Winicour metric also describes the exterior gravitational field of a scalar star, naked singularities as well as scalar star lenses, if these exist in nature, will serve as more efficient cosmic telescopes than regular gravitational lenses.
The naked mole-rat is the longest living rodent with a maximum lifespan exceeding 28 years. In addition to its longevity, naked mole-rats have an extraordinary resistance to cancer as tumors have never been observed in these rodents. Furthermore, we show that a combination of activated Ras and SV40 LT fails to induce robust anchorage-independent growth in naked mole-rat cells, while it readily transforms mouse fibroblasts. The mechanisms responsible for the cancer resistance of naked mole-rats were unknown. Here we show that naked mole-rat fibroblasts display hypersensitivity to contact inhibition, a phenomenon we termed "early contact inhibition." Contact inhibition is a key anticancer mechanism that arrests cell division when cells reach a high density. In cell culture, naked mole-rat fibroblasts arrest at a much lower density than those from a mouse. We demonstrate that early contact inhibition requires the activity of p53 and pRb tumor suppressor pathways. Inactivation of both p53 and pRb attenuates early contact inhibition. Contact inhibition in human and mouse is triggered by the induction of p27(Kip1). In contrast, early contact inhibition in naked mole-rat is associated with the induction of p16(Ink4a). Furthermore, we show that the roles of p16(Ink4a) and p27(Kip1) in the control of contact inhibition became temporally separated in this species: the early contact inhibition is controlled by p16(Ink4a), and regular contact inhibition is controlled by p27(Kip1). We propose that the additional layer of protection conferred by two-tiered contact inhibition contributes to the remarkable tumor resistance of the naked mole-rat.
We investigate here the occurrence and nature of a naked singularity for the inhomogeneous gravitational collapse of Tolman-Bondi dust clouds. It is shown that the naked singularities form at the center of the collapsing cloud in a wide class of collapse models, which includes the earlier cases considered by Eardley and Smarr and Christodoulou. This class also contains self-similar as well as non-self-similar models. The structure and strength of this singularity are examined, and the question is investigated as to when a nonzero measure set of nonspacelike trajectories could be emitted from the singularity, as opposed to isolated trajectories coming out. It is seen that the weak energy condition and positivity of energy density ensures that the families of nonspacelike trajectories come out of the singularity. The curvature strength of the naked singularity is examined, which provides an important test for its physical significance. This is done in terms of the strong curvature condition, which ensures that all the volume forms must be crushed to zero size in the limit of approach to the singularity, and, also, the divergence of the Kretschmann scalar $\mathcal{K}={R}^{\mathrm{abcd}}{R}_{\mathrm{abcd}}$ is pointed out. We show that the class considered here contains subclasses of solutions which admit strong curvature naked singularities in either of the senses stated above. The conditions are discussed for the naked singularity to be globally naked. An implication for the fundamental issue of the final fate of gravitational collapse is that naked singularities need not be considered as artifacts of geometric symmetries of space-time such as self-similarity, but arise in a wide range of gravitational collapse scenarios once the inhomogeneities in the matter distribution are taken into account. It is argued that a physical formulation for the cosmic censorship may be evolved which avoids the features above. Possibilities in this direction are suggested while indicating that the analysis presented here should be useful for any possible rigorous formulation of the cosmic censorship hypothesis.
We compare shadows cast by Schwarzschild black holes with those produced by two classes of naked singularities that result from gravitational collapse of spherically symmetric matter. The latter models consist of an interior naked singularity spacetime restricted to radii $r\leq R_b$, matched to Schwarzschild spacetime outside the boundary radius $R_b$. While a black hole always has a photon sphere and always casts a shadow, we find that the naked singularity models have photon spheres only if a certain parameter $M_0$ that characterizes these models satisfies $M_0\geq 2/3$, or equivalently, if $R_b\leq 3M$, where $M$ is the total mass of the object. Such models do produce shadows. However, models with $M_0<2/3$ (or $R_b>3M$) have no photon sphere and do not produce a shadow. Instead, they produce an interesting `full-moon' image. These results imply that the presence of a shadow does not by itself prove that a compact object is necessarily a black hole. The object could be a naked singularity with $M_0\geq 2/3$, and we will need other observational clues to distinguish the two possibilities. On the other hand, the presence of a full-moon image would certainly rule out a black hole and might suggest a naked singularity with $M_0<2/3$. It would be worthwhile to generalize the present study, which is restricted to spherically symmetric models, to rotating black holes and naked singularities.
BACKGROUND: Dermoscopy is a noninvasive technique that enables the clinician to perform direct microscopic examination of diagnostic features, not seen by the naked eye, in pigmented skin lesions. Diagnostic accuracy of dermoscopy has previously been assessed in meta-analyses including studies performed in experimental and clinical settings. OBJECTIVES: To assess the diagnostic accuracy of dermoscopy for the diagnosis of melanoma compared with naked eye examination by performing a meta-analysis exclusively on studies performed in a clinical setting. METHODS: We searched for publications from 1987 to January 2008 and found nine eligible studies. The selected studies compare diagnostic accuracy of dermoscopy with naked eye examination using a valid reference test on consecutive patients with a defined clinical presentation, performed in a clinical setting. Hierarchical summary receiver operator curve analysis was used to estimate the relative diagnostic accuracy for clinical examination with, and without, the use of dermoscopy. RESULTS: We found the relative diagnostic odds ratio for melanoma, for dermoscopy compared with naked eye examination, to be 15.6 [95% confidence interval (CI) 2.9-83.7, P = 0.016]; removal of two outlier studies changed this to 9.0 (95% CI 1.5-54.6, P = 0.03). CONCLUSIONS: Dermoscopy is more accurate than naked eye examination for the diagnosis of cutaneous melanoma in suspicious skin lesions when performed in the clinical setting.
This volume brings together more than a decade of information collected in the field and lab on the naked mole-rat (Heterocephalus glaber), a northeast African mammal unique for its physical characteristics and eusociality. Nearly blind and virtually hairless, naked mole-rats inhabit large subterranean colonies in which only one female and her one to three mates conceive offspring, while the young from previous litters maintain and defend the group as do workers in colonies of the social insects. In this first major treatise on naked mole-rats an international group of researchers covers such topics as the evolution of eusociality, phylogeny and systematics of the rodent family Bathyergidae, population and behavioral ecology and genetics of naked mole-rats in the field, vocal and nonvocal behaviors, social organization and divisions of labor within colonies, and climatic, social, and physiological factors affecting growth, reproduction, and reproductive suppression.In addition to the editors, the contributors are D. H. Abbott, M. W. Allard, N. C. Bennett, R. A. Brett, S. H. Braude, B. Crespi, S. V. Edwards, C. G. Faulkes, L. M. George, R. L. Honeycutt, E. A. Lacey, C. E. Liddell, E. McDaid, K. Nelson, K. M. Noonan, J. O'Riain, J. W. Pepper, H. K. Reeve, and D. A. Schlitter.
We calculate the {\\it afterglow} emission for Gamma-Ray Bursts (GRBs) going off in an extremely low density medium, referred to as {\\it naked bursts}. Our results also apply to the case where the external medium density falls off sharply at some distance from the burst. The observed afterglow flux in this case originates at high latitudes, i.e. where the angle between the fluid velocity and the observer line of sight is greater than $\\Gamma^{-1}$. The observed peak frequency of the spectrum for naked bursts decreases with observer time as $t^{-1}$, and the flux at the peak of the spectrum falls off as $t^{-2}$. The 2--10 keV $X$-ray flux from a naked burst of average fluence should be observable by the SWIFT satellite for time duration of about $10^3$ longer than the burst variability timescale. The high latitude emission contributes to the early $X$-ray afterglow flux for any GRB, not just naked bursts, and can be separated from the shocked inter-stellar medium (ISM) emission by their different spectral and temporal properties. Measurements of the high latitude emission could be used to map the angular structure of GRB producing shells.
) social and subterranean lifestyle generates a hypoxic niche. Under experimental conditions, naked mole-rats tolerate hours of extreme hypoxia and survive 18 minutes of total oxygen deprivation (anoxia) without apparent injury. During anoxia, the naked mole-rat switches to anaerobic metabolism fueled by fructose, which is actively accumulated and metabolized to lactate in the brain. Global expression of the GLUT5 fructose transporter and high levels of ketohexokinase were identified as molecular signatures of fructose metabolism. Fructose-driven glycolytic respiration in naked mole-rat tissues avoids feedback inhibition of glycolysis via phosphofructokinase, supporting viability. The metabolic rewiring of glycolysis can circumvent the normally lethal effects of oxygen deprivation, a mechanism that could be harnessed to minimize hypoxic damage in human disease.
As cities have gentrified, educated urbanites have come to prize what they regard as "authentic" urban life: aging buildings, art galleries, small boutiques, upscale food markets, neighborhood old-timers, funky ethnic restaurants, and old, family-owned shops. These signify a place's authenticity, in contrast to the bland standardization of the suburbs and exurbs. But as Sharon Zukin shows in Naked City, the rapid and pervasive demand for authenticity--evident in escalating real estate prices, expensive stores, and closely monitored urban streetscapes--has helped drive out the very people who first lent a neighborhood its authentic aura: immigrants, the working class, and artists. Zukin traces this economic and social evolution in six archetypal New York areas--Williamsburg, Harlem, the East Village, Union Square, Red Hook, and the city's community gardens--and travels to both the city's first IKEA store and the World Trade Center site. She shows that for followers of Jane Jacobs, this transformation is a perversion of what was supposed to happen. Indeed, Naked City is a sobering update of Jacobs' legendary 1961 book, The Death and Life of Great American Cities. Like Jacobs, Zukin looks at what gives neighborhoods a sense of place, but argues that over time, the emphasis on neighborhood distinctiveness has become a tool of economic elites to drive up real estate values and effectively force out the neighborhood "characters" that Jacobs so evocatively idealized.
We have previously shown that the intramuscular injection of naked plasmid DNA enables foreign gene expression in muscle. Further studies showed that the intravascular delivery of naked plasmid DNA enables high levels of expression not only in muscle but also in hepatocytes. For the liver, this technique required injection directly into the liver vessels (portal vein, hepatic vein, or bile duct) and occlusion of outflow. The present study now demonstrates that high levels of plasmid DNA expression in hepatocytes can be easily obtained by tail vein injections. The highest levels of expression are achieved by rapidly injecting the plasmid DNA in large volumes, approximately 2.5 ml. This technique has great potential for a wide variety of laboratory studies.
The current outbreak of the pandemic coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) demands its rapid, convenient, and large-scale diagnosis to downregulate its spread within as well as across the communities. But the reliability, reproducibility, and selectivity of majority of such diagnostic tests fail when they are tested either to a viral load at its early representation or to a viral gene mutated during its current spread. In this regard, a selective "naked-eye" detection of SARS-CoV-2 is highly desirable, which can be tested without accessing any advanced instrumental techniques. We herein report the development of a colorimetric assay based on gold nanoparticles (AuNPs), when capped with suitably designed thiol-modified antisense oligonucleotides (ASOs) specific for N-gene (nucleocapsid phosphoprotein) of SARS-CoV-2, could be used for diagnosing positive COVID-19 cases within 10 min from the isolated RNA samples. The thiol-modified ASO-capped AuNPs agglomerate selectively in the presence of its target RNA sequence of SARS-CoV-2 and demonstrate a change in its surface plasmon resonance. Further, the addition of RNaseH cleaves the RNA strand from the RNA-DNA hybrid leading to a visually detectable precipitate from the solution mediated by the additional agglomeration among the AuNPs. The selectivity of the assay has been monitored in the presence of MERS-CoV viral RNA with a limit of detection of 0.18 ng/μL of RNA having SARS-CoV-2 viral load. Thus, the current study reports a selective and visual "naked-eye" detection of COVID-19 causative virus, SARS-CoV-2, without the requirement of any sophisticated instrumental techniques.
The injection of naked plasmid DNA directly into the muscle cells of mice has been shown to induce potent humoral and cellular immune responses. The generation of a cytotoxic T lymphocyte (CTL) response after plasmid DNA injection may involve the presentation of the expressed antigen in the context of the injected myocytes' endogenous major histocompatibility (MHC)-encoded class I molecules or may use the MHC molecules of bone marrow-derived antigen presenting cells (APC) which are capable of providing co-stimulation as well. To resolve which cell type provides the specific restricting element for this method of vaccination we generated parent-->F1 bone marrow chimeras in which H-2bxd recipient mice received bone marrow that expressed only H-2b or H-2d MHC molecules. These mice were injected intramuscularly with naked plasmid DNA that encoded the nucleoprotein from the A/PR/8/34 influenza strain, which as a single antigen has epitopes for both H-2Db and H-2Kd. The resulting CTL responses were restricted to the MHC haplotype of the bone marrow alone and not to the second haplotype expressed by the recipient's myocytes. The role of somatic tissues that express protein from injected plasmids may be to serve as a reservoir for that antigen which is then transferred to the APC. Consequently, our data show that the mechanism of priming in this novel method for vaccination uses the MHC from bone marrow-derived APC, which are efficient at providing all of the necessary signals for priming the T cell.
Tremendous variation in maximum life span among species overshadows modest increases in longevity resulting from experimental manipulation. Few aging studies focus on long-lived mammals even though these species may expose mechanisms involved in resisting aging. Naked mole-rats (NMRs approximately 35 grams) are the longest-living (>28.3 years) rodents known. This review describes their biology and potential use in aging research. Lifestyle features concur with most evolutionary theories with the exception of the disposable soma theory. Indeed, maximum life span is similar in breeders and nonbreeders, and these highly fecund animals reproduce until they die. Shared characteristics with calorie-restricted, methionine-restricted, and dwarf mice models of extended longevity include reduced body temperature; reduced thyroid, and blood glucose concentrations; and low glycated hemoglobin; in addition to reduced incidence of cancer. Young naked mole-rats surprisingly have high levels of accrued oxidative damage. With their similar longevity quotient to humans, these rodents may provide a novel opportunity to examine mechanisms modulating aging.
Using the technique of DNA fingerprinting, we investigated the genetic structure within and among four wild-caught colonies (n = 50 individuals) of a eusocial mammal, the naked mole-rat (Heterocephalus glaber; Rodentia: Bathyergidae). We found that DNA fingerprints of colony-mates were strikingly similar and that between colonies they were much more alike than fingerprints of non-kin in other free-living vertebrates. Extreme genetic similarity within colonies is due to close genetic relationship (mean relatedness estimate +/- SE, r = 0.81 +/- 0.10), which apparently results from consanguineous mating. The inbreeding coefficient (F = 0.45 +/- 0.18) is the highest yet recorded among wild mammals. The genetic structure of naked mole-rat colonies lends support to kin selection and ecological constraints models for the evolution of cooperative breeding and eusociality.
Here is the Naked Ape at his most primal - in love, at work, at war. Meet man as he really is: relative to the apes, stripped of his veneer as we see him courting, making love, sleeping, socialising, grooming, playing. Zoologist Desmond Morris's classic takes its place alongside Darwin's Origin of the Species, presenting man not as a fallen angel, but as a risen ape, remarkable in his resilience, energy and imagination, yet an animal nonetheless, in danger of forgetting his origins. With its penetrating insights on man's beginnings, sex life, habits and our astonishing bonds to the animal kingdom, The Naked Ape is a landmark, at once provocative, compelling and timeless.
Christodoulou's recent analysis (1984) of naked singularities in time-symmetric Tolman-Bondi collapse is simplified and generalised to a wider class of Tolman-Bondi models. The strengths of the naked singularities are assessed in terms of limiting focusing conditions.
Five studies tested the idea that people are reluctant to make proplaintiff liability decisions when the plaintiffs evidence is based on naked statistical evidence alone. Students (n = 740) and experienced trial judges (M = 111) averaged fewer than 10% affirmative decisions of liability when a case was based on naked statistical evidence but averaged over 65% affirmative decisions based on other forms of evidence even though the mathematical and subjective probabilities were the same for both types of evidence. Numerous hypotheses, including causal relevance, linkage to the specific case, and fairness to the defendant proved inadequate to explain the data. For evidence to affect decisions, the evidence must do more than affect people's perceptions about the probabilities associated with the ultimate fact; people seem to require that suppositions regarding the ultimate fact affect their perceptions of the truth or falsity of the evidence.
Currently, antibiotic resistance and cancer are two of the most important public health problems killing more than ∼1.5 million people annually, showing that antibiotics and current chemotherapeutics are not as effective as they were in the past. Nanotechnology is presented here as a potential solution. However, current protocols for the traditional physicochemical synthesis of nanomaterials are not free of environmental and social drawbacks, often involving the use of toxic catalysts. This article shows the production of pure naked selenium nanoparticles (SeNPs) by a novel green process called pulsed laser ablation in liquids (PLAL). After the first set of irradiations, another set was performed to reduce the size below 100 nm, which resulted in a colloidal solution of spherical SeNPs with two main populations having sizes around ∼80 and ∼10 nm. The particles after the second set of irradiations also showed higher colloidal stability. SeNPs showed a dose-dependent antibacterial effect toward both standard and antibiotic-resistant phenotypes of Gram-negative and Gram-positive bacteria at a range of concentrations between 0.05 and 25 ppm. Besides, the SeNPs showed a low cytotoxic effect when cultured with human dermal fibroblasts cells at a range of concentrations up to 1 ppm while showing an anticancer effect toward human melanoma and glioblastoma cells at the same concentration range. This article therefore introduces the possibility of using totally naked SeNPs synthesized by a new PLAL protocol as a novel and efficient nanoparticle fabrication process for biomedical applications.