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1.
Rev Sci Instrum ; 87(11): 11D810, 2016 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-27910490

RESUMO

We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 µm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime.

2.
Phys Rev Lett ; 116(14): 141103, 2016 04 08.
Artigo em Inglês | MEDLINE | ID: mdl-27104694

RESUMO

For 50 years, cosmic-ray air showers have been detected by their radio emission. We present the first laboratory measurements that validate electrodynamics simulations used in air shower modeling. An experiment at SLAC provides a beam test of radio-frequency (rf) radiation from charged particle cascades in the presence of a magnetic field, a model system of a cosmic-ray air shower. This experiment provides a suite of controlled laboratory measurements to compare to particle-level simulations of rf emission, which are relied upon in ultrahigh-energy cosmic-ray air shower detection. We compare simulations to data for intensity, linearity with magnetic field, angular distribution, polarization, and spectral content. In particular, we confirm modern predictions that the magnetically induced emission in a dielectric forms a cone that peaks at the Cherenkov angle and show that the simulations reproduce the data within systematic uncertainties.

3.
Chem Sci ; 5(9): 3528-3535, 2014 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-25580213

RESUMO

We describe a one-pot strategy for the high yielding, operationally simple synthesis of fluorescent probes for Zn2+ that bear biological targeting groups and exemplify the utility of our method through the preparation of a small library of sensors. Investigation of the fluorescence behaviour of our library revealed that although all behaved as expected in MeCN, under biologically relevant conditions in HEPES buffer, a plasma membrane targeting sensor displayed a dramatic switch on response to excess Zn2+ as a result of aggregation phenomena. Excitingly, in cellulo studies in mouse pancreatic islets demonstrated that this readily available sensor was indeed localised to the exterior of the plasma membrane and clearly responded to the Zn2+ co-released when the pancreatic beta cells were stimulated to release insulin. Conversely, sensors that target intracellular compartments were unaffected. These results demonstrate that this sensor has the potential to allow the real time study of insulin release from living cells and exemplifies the utility of our simple synthetic approach.

4.
Phys Rev Lett ; 109(7): 074801, 2012 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-23006375

RESUMO

We report generation of density modulation at terahertz (THz) frequencies in a relativistic electron beam through laser modulation of the beam longitudinal phase space. We show that by modulating the energy distribution of the beam with two lasers, density modulation at the difference frequency of the two lasers can be generated after the beam passes through a chicane. In this experiment, density modulation around 10 THz was generated by down-converting the frequencies of an 800 nm laser and a 1550 nm laser. The central frequency of the density modulation can be tuned by varying the laser wavelengths, beam energy chirp, or momentum compaction of the chicane. This technique can be applied to accelerator-based light sources for generation of coherent THz radiation and marks a significant advance toward tunable narrow band THz sources.

5.
Phys Rev Lett ; 108(2): 024802, 2012 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-22324690

RESUMO

Echo-enabled harmonic generation free electron lasers hold great promise for the generation of fully coherent radiation in x-ray wavelengths. Here we report the first evidence of high harmonics from the echo-enabled harmonic generation technique in the realistic scenario where the laser energy modulation is comparable to the beam slice energy spread. In this experiment, coherent radiation at the seventh harmonic of the second seed laser is generated when the energy modulation amplitude is about 2-3 times the slice energy spread. The experiment confirms the underlying physics of echo-enabled harmonic generation and may have a strong impact on emerging seeded x-ray free electron lasers that are capable of generating laserlike x rays which will advance many areas of science.

6.
Phys Rev Lett ; 105(11): 114801, 2010 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-20867575

RESUMO

We report the first experimental demonstration of the echo-enabled harmonic generation technique, which holds great promise for generation of high-power, fully coherent short-wavelength radiation. In this experiment, coherent radiation at the 3rd and 4th harmonics of the second seed laser is generated from the so-called beam echo effect. The experiment confirms the physics behind this technique and paves the way for applying the echo-enabled harmonic generation technique for seeded x-ray free electron lasers.

7.
Phys Rev Lett ; 88(19): 194801, 2002 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-12005637

RESUMO

Electron beams with the lowest, normalized transverse emittance recorded so far were produced and confirmed in single-bunch-mode operation of the Accelerator Test Facility at KEK. We established a tuning method of the damping ring which achieves a small vertical dispersion and small x-y orbit coupling. The vertical emittance was less than 1% of the horizontal emittance. At the zero-intensity limit, the vertical normalized emittance was less than 2.8 x 10(-8) rad m at beam energy 1.3 GeV. At high intensity, strong effects of intrabeam scattering were observed, which had been expected in view of the extremely high particle density due to the small transverse emittance.

8.
Lancet ; 354(9184): 1091-2, 1999 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-10509502

RESUMO

After the introduction of a Haemophilus Influenzae type b (Hib) conjugate vaccine into The Gambia, the annual incidence of Hib meningitis has fallen from more than 200 per 100,000 before vaccination to 21 per 100,000 during the past 12 months.


Assuntos
Vacinas Anti-Haemophilus , Haemophilus influenzae tipo b , Meningite por Haemophilus/epidemiologia , Gâmbia/epidemiologia , Humanos , Incidência , Lactente , Meningite por Haemophilus/prevenção & controle , Vacinas Conjugadas
10.
Lancet ; 349(9060): 1191-7, 1997 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-9130939

RESUMO

BACKGROUND: In developing countries, pneumonia and meningitis due to Haemophilus influenzae type b (Hib) are common in children under age 12 months and the mortality from meningitis is high. Protein-polysaccharide conjugate vaccines have brought Hib disease under control in industrialised countries. We did a double-blind randomised trial in The Gambia to assess the efficacy of a Hib conjugate vaccine for the prevention of meningitis, pneumonia, and other invasive diseases due to Hib. METHODS: Between March, 1993, and October, 1995, 42,848 infants were randomly allocated the conjugate vaccine Hib polysaccharide tetanus protein (PRP-T) mixed with diphtheria-tetanus-pertussis vaccine (DTP), or DTP alone at age 2 months, 3 months, and 4 months. Children who presented with signs of invasive Hib were investigated by blood culture and, where appropriate, by lumbar puncture, chest radiograph, or percutaneous lung aspirate. Children were followed up for between 5 and 36 months. FINDINGS: The median ages at which children received the study vaccine were 11 weeks, 18 weeks, and 24 weeks. 83% of children enrolled received all three doses of vaccine. 17 cases of culture-positive Hib pneumonia, 28 of Hib meningitis, and five of other forms of invasive Hib disease were detected amongst the study children. The efficacy of the vaccine for the prevention of all invasive disease after three doses was 95% (PRP-T vaccinees 1, controls 19 [95% CI 67-100]), for the prevention of Hib pneumonia after two or three doses, 100% (vaccinees 0, controls 10 [55-100]), and for the prevention of radiologically defined pneumonia at any time after enrollment, 21.1% (PRP-T vaccinees 198, controls 251 [4.6-34.9]). INTERPRETATION: PRP-T conjugate Hib vaccine prevented most cases of meningitis and pneumonia due to Hib in Gambian infants. The reduction in the overall incidence of radiologically defined pneumonia in PRP-T vaccinees suggests that about 20% of episodes of pneumonia in young Gambian children are due to Hib. The introduction of Hib vaccines into developing countries should substantially reduce childhood mortality due to pneumonia and meningitis.


Assuntos
Infecções por Haemophilus/prevenção & controle , Vacinas Anti-Haemophilus , Haemophilus influenzae , Meningite por Haemophilus/prevenção & controle , Pneumonia Bacteriana/prevenção & controle , Toxoide Tetânico , Vacinas Conjugadas , Fatores Etários , Países em Desenvolvimento , Vacina contra Difteria, Tétano e Coqueluche/administração & dosagem , Método Duplo-Cego , Seguimentos , Gâmbia , Infecções por Haemophilus/diagnóstico , Vacinas Anti-Haemophilus/administração & dosagem , Haemophilus influenzae/classificação , Humanos , Esquemas de Imunização , Incidência , Lactente , Meningite por Haemophilus/diagnóstico , Paracentese , Pneumonia Bacteriana/diagnóstico , Radiografia Torácica , Punção Espinal , Toxoide Tetânico/administração & dosagem , Vacinas Conjugadas/administração & dosagem
11.
Resuscitation ; 31(3): 255-63, 1996 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-8783411

RESUMO

OBJECTIVE: To determine how frequently reports of research in human cardiopulmonary resuscitation mention approval by a research ethics committee and address subjects' consent. METHODS: Retrospective review of published reports of interventional research in human cardiopulmonary resuscitation. Reports were retrieved from the MEDLINE database and selected according to pre-established criteria. Data were abstracted independently by the two authors with differences resolved by mutual agreement. Results were analyzed according to whether the research took place in the prehospital setting, the emergency department, or the hospital; whether it was conducted within or outside the United States; whether it received any funding from the US government; its randomization scheme; the year of publication; and whether the journal's instructions required mention of REC approval or subjects' consent. RESULTS: Reports of 47 studies met our criteria for inclusion. Of these, 24 (51%) mentioned approval by a research ethics committee and 12 (26%) addressed subjects' consent. Significantly more studies reported ethics committee approval or addressed consent during more recent years. Authors were more likely to report consent, REC approval, or both when journal instructions required that REC approval be mentioned. CONCLUSION: Reports of resuscitation research have not consistently mentioned approval from a research ethics committee or addressed subjects' consent for interventional studies using human subjects. However, they are doing so more frequently in recent years as journal requirements for reporting change. REC approval is now almost always being reported, but subjects' consent is often not addressed. Journal editors and reviewers should ensure that authors adhere to the journal's instructions about reporting ethical conduct of experiments.


Assuntos
Comissão de Ética , Consentimento Livre e Esclarecido , Projetos de Pesquisa , Ressuscitação , Adulto , Reanimação Cardiopulmonar , Serviços Médicos de Emergência , Serviço Hospitalar de Emergência , Ética Médica , Financiamento Governamental , Hospitalização , Humanos , Publicações Periódicas como Assunto , Editoração , Ensaios Clínicos Controlados Aleatórios como Assunto , Apoio à Pesquisa como Assunto , Estudos Retrospectivos , Estados Unidos
12.
Bull World Health Organ ; 62(5): 729-36, 1984.
Artigo em Inglês | MEDLINE | ID: mdl-6334570

RESUMO

The total cost of the Expanded Programme on Immunization and of its various components in the Gambia over a period of one year (from July 1980 to June 1981) was investigated, and the costs per immunization dose and per fully immunized child were calculated. The total costs were to a large extent (45%) due to the cost of personnel and fixed costs. Where there was efficient delivery of immunizations, the average cost per dose was about one-fifth of that in the most costly facilities (range: US$2.32 to $0.41). The lower costs were related to more intensive use of the facilities. The national average cost was $1.09. The implications of the results of this study for policies to reduce costs are discussed, and further areas of research are suggested that will provide improved information to guide decision-makers in the use of scarce immunization programme resources for better health in the world.


Assuntos
Imunização/economia , Criança , Pré-Escolar , Custos e Análise de Custo , Gâmbia , Política de Saúde , Humanos , Lactente , Serviços Preventivos de Saúde/economia , Serviços Preventivos de Saúde/estatística & dados numéricos
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