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1.
Nature ; 503(7475): 238-41, 2013 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-24196713

RESUMO

Most large (over a kilometre in diameter) near-Earth asteroids are now known, but recognition that airbursts (or fireballs resulting from nuclear-weapon-sized detonations of meteoroids in the atmosphere) have the potential to do greater damage than previously thought has shifted an increasing portion of the residual impact risk (the risk of impact from an unknown object) to smaller objects. Above the threshold size of impactor at which the atmosphere absorbs sufficient energy to prevent a ground impact, most of the damage is thought to be caused by the airburst shock wave, but owing to lack of observations this is uncertain. Here we report an analysis of the damage from the airburst of an asteroid about 19 metres (17 to 20 metres) in diameter southeast of Chelyabinsk, Russia, on 15 February 2013, estimated to have an energy equivalent of approximately 500 (±100) kilotons of trinitrotoluene (TNT, where 1 kiloton of TNT = 4.185×10(12) joules). We show that a widely referenced technique of estimating airburst damage does not reproduce the observations, and that the mathematical relations based on the effects of nuclear weapons--almost always used with this technique--overestimate blast damage. This suggests that earlier damage estimates near the threshold impactor size are too high. We performed a global survey of airbursts of a kiloton or more (including Chelyabinsk), and find that the number of impactors with diameters of tens of metres may be an order of magnitude higher than estimates based on other techniques. This suggests a non-equilibrium (if the population were in a long-term collisional steady state the size-frequency distribution would either follow a single power law or there must be a size-dependent bias in other surveys) in the near-Earth asteroid population for objects 10 to 50 metres in diameter, and shifts more of the residual impact risk to these sizes.

2.
Nature ; 458(7237): 485-8, 2009 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-19325630

RESUMO

In the absence of a firm link between individual meteorites and their asteroidal parent bodies, asteroids are typically characterized only by their light reflection properties, and grouped accordingly into classes. On 6 October 2008, a small asteroid was discovered with a flat reflectance spectrum in the 554-995 nm wavelength range, and designated 2008 TC(3) (refs 4-6). It subsequently hit the Earth. Because it exploded at 37 km altitude, no macroscopic fragments were expected to survive. Here we report that a dedicated search along the approach trajectory recovered 47 meteorites, fragments of a single body named Almahata Sitta, with a total mass of 3.95 kg. Analysis of one of these meteorites shows it to be an achondrite, a polymict ureilite, anomalous in its class: ultra-fine-grained and porous, with large carbonaceous grains. The combined asteroid and meteorite reflectance spectra identify the asteroid as F class, now firmly linked to dark carbon-rich anomalous ureilites, a material so fragile it was not previously represented in meteorite collections.

3.
Science ; 290(5490): 320-5, 2000 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-11030647

RESUMO

The preatmospheric mass of the Tagish Lake meteoroid was about 200,000 kilograms. Its calculated orbit indicates affinity to the Apollo asteroids with a semimajor axis in the middle of the asteroid belt, consistent with a linkage to low-albedo C, D, and P type asteroids. The mineralogy, oxygen isotope, and bulk chemical composition of recovered samples of the Tagish Lake meteorite are intermediate between CM and CI meteorites. These data suggest that the Tagish Lake meteorite may be one of the most primitive solar system materials yet studied.

4.
J Neuroimmunol ; 125(1-2): 103-13, 2002 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-11960646

RESUMO

Ntera2/D1 cells had an A1 B8 Bw6 Cw7 DR3 DR52 major histocompatibility complex (MHC) genotype. Its neuronal derivative, hNT neurons, expressed A1 B8 Bw6 MHC class I molecules, but did not activate, and its hNT supernatant suppressed allogeneic mixed lymphocyte cultures (MLC) >98% (p<0.01), phytohemagglutinin (PHA)-activated T-cell proliferation >87% (p<0.01), even 48 h after stimulation, suppressed phorbol 12-myristate 13-acetate (PMA)/ionomycin-induced T-cell proliferation >99% (p<0.001), and reduced interleukin-2 (IL-2) production (p<0.01), while maintaining T cells in a quiescent G(0)/G(1) state without lowering their viability. This immunosuppressive activity was attributed to a 40-100-kDa anionic hNT protein with an isoelectric point of 4.8.


Assuntos
Interleucina-2/biossíntese , Neurônios/imunologia , Linfócitos T/citologia , Linfócitos T/metabolismo , Transplante de Tecido Encefálico/imunologia , Comunicação Celular/imunologia , Divisão Celular/imunologia , Meios de Cultivo Condicionados , Expressão Gênica/imunologia , Antígenos de Histocompatibilidade Classe I/genética , Humanos , Ativação Linfocitária/imunologia , Células-Tronco Neoplásicas/citologia , Células-Tronco Neoplásicas/imunologia , Neurônios/citologia , Linfócitos T/imunologia , Células Tumorais Cultivadas
6.
J Neurosurg ; 92(2 Suppl): 214-6, 2000 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-10763695

RESUMO

The intradural myolipoma is a very rare tumor, consisting of fully differentiated striated muscle fibers mingled with fat. Only four previous cases have been identified. The authors present a case in which this tumor was associated with a symptomatic tethered spinal cord in an 18-year-old man.


Assuntos
Lipoma/cirurgia , Defeitos do Tubo Neural/cirurgia , Neoplasias da Medula Espinal/cirurgia , Adolescente , Diagnóstico Diferencial , Humanos , Lipoma/congênito , Lipoma/diagnóstico , Lipoma/patologia , Imageamento por Ressonância Magnética , Masculino , Defeitos do Tubo Neural/diagnóstico , Defeitos do Tubo Neural/patologia , Medula Espinal/patologia , Medula Espinal/cirurgia , Neoplasias da Medula Espinal/congênito , Neoplasias da Medula Espinal/diagnóstico , Neoplasias da Medula Espinal/patologia , Vértebras Torácicas/anormalidades , Vértebras Torácicas/patologia , Vértebras Torácicas/cirurgia
12.
Pediatr Neurosurg ; 32(4): 170-5, 2000 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-10940766

RESUMO

Trampolines were responsible for over 6,500 pediatric cervical spine injuries in 1998. This represents a five-fold increase in just 10 years. While most have been minor, paraplegia, quadriplegia and death are all reported. We present 2 cases of trampoline-related cervical spine injury and review the relevant literature. Additionally, we examine the efforts made to reduce the incidence of trampoline injuries, and discuss why these have failed. We conclude that safety guidelines and warnings are inadequate. In addition, we support recommendations for a ban on the use of trampolines by children.


Assuntos
Traumatismos em Atletas/prevenção & controle , Vértebras Cervicais/lesões , Luxações Articulares/etiologia , Lesões do Pescoço/etiologia , Fraturas da Coluna Vertebral/etiologia , Fenômenos Biomecânicos , Braquetes , Vértebras Cervicais/diagnóstico por imagem , Criança , Humanos , Luxações Articulares/diagnóstico por imagem , Masculino , Lesões do Pescoço/diagnóstico por imagem , Radiografia , Fraturas da Coluna Vertebral/diagnóstico por imagem , Resultado do Tratamento
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