13,803 research outputs found
Magnetic trapping and Zeeman relaxation of imidogen (NH X-triplet-Sigma)
Imidogen (NH) radicals are magnetically trapped and their Zeeman relaxation
and energy transport collision cross sections with helium are measured.
Continuous buffer-gas loading of the trap is direct from a room-temperature
molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically
trapped electronic, vibrational and rotational ground state imidogen in
collisions with He-3 is measured to be 3.8 +/- 1.1 E-19 cm^2 at 710 mK. The
NH-He energy transport cross section is also measured, indicating a ratio of
diffusive to inelastic cross sections of gamma = 7 E4 in agreement with the
recent theory of Krems et al. (PRA 68 051401(R) (2003))Comment: 12 pages, 3 figure
Time-Domain Measurement of Spontaneous Vibrational Decay of Magnetically Trapped NH
The v = 1 -> 0 radiative lifetime of NH (X triplet-Sigma-, v=1,N=0) is
determined to be tau_rad,exp. = 37.0 +/- 0.5 stat +2.0 / -0.8 sys miliseconds,
corresponding to a transition dipole moment of |mu_10| = 0.0540 + 0.0009 /
-0.0018 Debye. To achieve the long observation times necessary for direct
time-domain measurement, vibrationally excited NH (X triplet-Sigma-, v=1,N=0)
radicals are magnetically trapped using helium buffer-gas loading. Simultaneous
trapping and lifetime measurement of both the NH(v=1, N=0) and NH(v=0,N=0)
populations allows for accurate extraction of tau_rad,exp. Background helium
atoms are present during our measurement of tau_rad,exp., and the rate constant
for helium atom induced collisional quenching of NH(v=1,N=0) was determined to
be k_q < 3.9 * 10^-15 cm^3/s. This bound on k_q yields the quoted systematic
uncertainty on tau_rad,exp. Using an ab initio dipole moment function and an
RKR potential, we also determine a theoretical value of 36.99 ms for this
lifetime, in agreement with our experimental value. Our results provide an
independent determination of tau_rad,10, test molecular theory, and furthermore
demonstrate the efficacy of buffer-gas loading and trapping in determining
metastable radiative and collisional lifetimes.Comment: 10 pages + 3 figures (11 pages total) v2 has minor corrections and
explanations accepted for publication in PR
Astrometric Discovery of GJ 164B
We discovered a low-mass companion to the M-dwarf GJ 164 with the CCD-based
imaging system of the Stellar Planet Survey (STEPS) astrometric program. The
existence of GJ 164B was confirmed with Hubble Space Telescope NICMOS imaging
observations. A high-dispersion spectral observation in V sets a lower limit of
delta m> 2.2 mag between the two components of the system. Based upon our
parallax value of 0.082 +/- 0.008, we derive the following orbital parameters:
P = 2.04 +/- 0.03 y, a = 1.03 +/- 0.03 AU, and Mtotal = 0.265 +/- 0.020 MSun.
The component masses are MA = 0.170 +/- 0.015 MSun and MB = 0.095 +/- 0.015
MSun. Based on its mass, colors, and spectral properties, GJ 164B has spectral
type M6-8 V.Comment: pdf file 14 pages with 6 fig
Giant Quantum Reflection of Neon Atoms from a Ridged Silicon Surface
The specular reflectivity of slow, metastable neon atoms from a silicon
surface was found to increase markedly when the flat surface was replaced by a
grating structure with parallel narrow ridges. For a surface with ridges that
have a sufficiently narrow top, the reflectivity was found to increase more
than two orders of magnitude at the incident angle of 10 mRad from the surface.
The slope of the reflectivity vs the incident angle near zero was found to be
nearly an order of magnitude smaller than that of a flat surface. A grating
with 6.5% efficiency for the first-order diffraction was fabricated by using
the ridged surface structure.Comment: 5 pages, 4 figures. To be published in J. Phys. Soc. Jp
CDS wide slit time-series of EUV coronal bright points
Wide slit (90" x 240" ) movies of four Extreme Ultraviolet coronal bright points (BPs) obtained with the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SoHO) have been inspected. The wavelet analysis of the He I 584.34 Ă
, O V 629.73 Ă
and Mg VII/IX 368 Ă
time-series confirms the oscillating nature of the BPs, with periods ranging between 600 and 1100 s. In one case we detect periods as short as 236 s. We suggest that these oscillations are the same as those seen in the chromospheric network and that a fraction of the network bright points are most likely the cool footpoints of the loops comprising coronal bright points. These oscillations are interpreted in terms of global acoustic modes of the closed magnetic structures associated with BPs
PreferĂȘncias nutricionais entre adolescentes da classe mĂ©dia de Manaus, AM (Brazil)
INTRODUĂĂO: O Brasil tem sido considerado um PaĂs em transição nutricional em razĂŁo dos recentes aumentos na prevalĂȘncia de obesidade e doenças crĂŽnicas na classe mĂ©dia, sendo importante identificar os fatores que influenciam as preferĂȘncias nutricionais desse grupo. Foi realizado estudo com estudantes de classe mĂ©dia de um colĂ©gio secundĂĄrio, particular, em Manaus, AM, Brasil. Com o objetivo de determinar a disponibilidade e a acessibilidade das merendas e analisar as atitudes e preferĂȘncias dos estudantes e a influĂȘncia de vĂĄrios fatores na escolha de merendas nutritivas. MĂTODOS: O estudo incluiu quatros fases: (a) discusĂŁo em um grupo de especialistas em nutrição sobre a disponibilidade e acessibilidade das merendas em Manaus; (b) inquĂ©rito junto a um grupo dos adolescentes (n=63) sobre suas preferĂȘncias e hĂĄbitos nutricionais; (c) inquĂ©rito junto a supermercados selecionado para identificar a disponibilidade e acessibilidade das merendas preferidas; (d) um grupo acompanhado de uma subamostra dos adolescentes (n=55) para identificar a preferĂȘncias e atitudes sobre o custo e disponibilidade das merendas. RESULTADOS: Foi constatado que os estudantes possuĂam condiçÔes financeiras para comprar merendas e que as merendas nutritivas nĂŁo custam mais do que as nĂŁo nutritivas. A preferĂȘncia dos adolescentes foi por merendas nĂŁo nutritivas. Os fatores que, principalmente, influenciam na escolha originam-se da famĂlia e da televisĂŁo. CONCLUSĂO: As implicaçÔes para futuras pesquisas e programas nutricionais sĂŁo discutidos, recomendando-se campanha de educação nutricional para famĂlias, visto a importĂąncia desta na escolha de merendas entre esses adolescentes.INTRODUCTION: Brazil has been called a nation in nutrition transitional because of recent increases in the prevalence of obesity and related chronic diseases. With overweight conditions already prevalent among middle-income populations, there exists a need to identify factors that influence nutrition behavior within this group. OBJECTIVE: To address this subject, a research study was implemented among middle-class adolescents attending a large private secondary school in Manaus, Amazonas, Brazil. The study determined the availability and accessibility of snack foods as well as subjects’ attitudes and preferences towards, and the influence of family and friends on healthy (high-nutrient density) snack choices. METHODS: The 4-stage process included: (a) a nutrition expert focus group discussion that reported local nutrition problems in general and factors related to adolescent nutrition, (b) an adolescent pilot survey (n=63) that solicited information about snacking preferences and habits as well as resources for nutrition information and snack money; (c) a survey of various area food market sources to determine the availability and accessibility of high nutrient density snacks; and (d) a follow-up adolescent survey (n=55) that measured snack food preferences and perceptions about their cost and availability. RESULTS: Results included the finding that, although affordable high nutrient density snacks were available, preferences for low nutrient density snacks prevailed. The adolescents were reportedly more likely to be influenced by and obtain nutrition information from family members than friends. CONCLUSION: From study results it is apparent that a focus on food availability will not automatically result in proper nutritional practices among adolescents. This fact and the parental influence detected are evidence of a need to involve adolescents and their parents in nutrition education campaigns to improve adolescent snack food choices
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