1,173 research outputs found
A high frequency optical trap for atoms using Hermite-Gaussian beams
We present an experimental method to create a single high frequency optical
trap for atoms based on an elongated Hermite-Gaussian TEM01 mode beam. This
trap results in confinement strength similar to that which may be obtained in
an optical lattice. We discuss an optical setup to produce the trapping beam
and then detail a method to load a Bose-Einstein Condensate (BEC) into a TEM01
trap. Using this method, we have succeeded in producing individual highly
confined lower dimensional condensates.Comment: 9 pages, 5 figure
Bose Einstein Condensate in a Box
Bose-Einstein condensates have been produced in an optical box trap. This
novel optical trap type has strong confinement in two directions comparable to
that which is possible in an optical lattice, yet produces individual
condensates rather than the thousands typical of a lattice. The box trap is
integrated with single atom detection capability, paving the way for studies of
quantum atom statistics.Comment: 4 pages, 5 figure
Direct Observation of Sub-Poissonian Number Statistics in a Degenerate Bose Gas
We report the direct observation of sub-Poissonian number fluctuation for a
degenerate Bose gas confined in an optical trap. Reduction of number
fluctuations below the Poissonian limit is observed for average numbers that
range from 300 to 60 atoms.Comment: 5 pages, 4 figure
Vegetation characterization through the use of precipitation-affected SAR signals
Current space-based SAR offers unique opportunities to classify vegetation types and to monitor vegetation growth due to its frequent acquisitions and its sensitivity to vegetation geometry. However, SAR signals also experience frequent temporal fluctuations caused by precipitation events, complicating the mapping and monitoring of vegetation. In this paper, we show that the influence of a priori known precipitation events on the signals can be used advantageously for the classification of vegetation conditions. For this, we exploit the change in Sentinel-1 backscatter response between consecutive acquisitions under varying wetness conditions, which we show is dependent on the state of vegetation. The performance further improves when a priori information on the soil type is taken into account.1010FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2013/50943-
A broken solar type II radio burst induced by a coronal shock propagating across the streamer boundary
We discuss an intriguing type II radio burst that occurred on 2011 March 27.
The dynamic spectrum was featured by a sudden break at about 43 MHz on the
well-observed harmonic branch. Before the break, the spectrum drifted gradually
with a mean rate of about -0.05 MHz/s. Following the break, the spectrum jumped
to lower frequencies. The post-break emission lasted for about three minutes.
It consisted of an overall slow drift which appeared to have a few fast drift
sub-bands. Simultaneous observations from the Solar TErrestrial RElations
Observatory (STEREO) and the Solar Dynamics Observatory (SDO) were also
available and are examined for this event. We suggest that the slow-drift
period before the break was generated inside a streamer by a coronal eruption
driven shock, and the spectral break as well as the relatively wide spectrum
after the break is a consequence of the shock crossing the streamer boundary
where density drops abruptly. It is suggested that this type of radio bursts
can be taken as a unique diagnostic tool for inferring the coronal density
structure, as well as the radio emitting source region.Comment: 12 pages, 5 figures, accepted by ApJ 201
Near-Limb Zeeman and Hanle Diagnostics
"Weak" magnetic-field diagnostics in faint objects near the bright solar disk
are discussed in terms of the level of non-object signatures, in particular, of
the stray light in telescopes. Calculated dependencies of the stray light
caused by diffraction at the 0.5-, 1.6-, and 4-meter entrance aperture are
presented. The requirements for micro-roughness of refractive and reflective
primary optics are compared. Several methods for reducing the stray light (the
Lyot coronagraphic technique, multiple stages of apodizing in the focal and
exit pupil planes, apodizing in the entrance aperture plane with a special
mask), and reducing the random and systematic errors are noted. An acceptable
level of stray light in telescopes is estimated for the V-profile recording
with a signal-to-noise ratio greater than three. Prospects for the limb
chromosphere magnetic measurements are indicated.Comment: 11 pages, 3 figure
Notions and subnotions in information structure
Three dimensions can be distinguished in a cross-linguistic account of information structure. First, there is the definition of the focus constituent, the part of the linguistic expression which is subject to some focus meaning. Second and third, there are the focus meanings and the array of structural devices that encode them. In a given language, the expression of focus is facilitated as well as constrained by the grammar within which the focus devices operate. The prevalence of focus ambiguity, the structural inability to make focus distinctions, will thus vary across languages, and within a language, across focus meanings
Surface Properties of the Half- and Full-Heusler Alloys
Using a full-potential \textit{ab-initio} technique I study the electronic
and magnetic properties of the (001) surfaces of the half-Heusler alloys,
NiMnSb, CoMnSb and PtMnSb and of the full-Heusler alloys CoMnGe, CoMnSi
and CoCrAl. The MnSb terminated surfaces of the half-Heusler compounds
present properties similar to the bulk compounds and, although the
half-metallicity is lost, an important spin-polarisation at the Fermi level. In
contrast to this the Ni terminated surface shows an almost zero net
spin-polarisation. While the bulk CoMnGe and CoMnSi are almost
half-ferromagnetic, their surfaces lose the half-metallic character and the net
spin-polarisation at the Fermi level is close to zero. Contrary to these
compounds the CrAl terminated (001) surface of CoCrAl shows a spin
polarisation of about 84%.Comment: 14 pages, 6 figure
Zingerone in the Flower of Passiflora maliformis Attracts an Australian Fruit Fly, Bactrocera jarvisi (Tryon)
Passiflora maliformis is an introduced plant in Australia but its flowers are known to attract the native Jarvis’s fruit fly, Bactrocera jarvisi (Tryon). The present study identifies and quantifies likely attractant(s) of male B. jarvisi in P. maliformis flowers. The chemical compositions of the inner and outer coronal filaments, anther, stigma, ovary, sepal, and petal of P. maliformis were separately extracted with ethanol and analyzed using gas chromatography-mass spectrometry (GC-MS). Polyisoprenoid lipid precursors, fatty acids and their derivatives, and phenylpropanoids were detected in P. maliformis flowers. Phenylpropanoids included raspberry ketone, cuelure, zingerone, and zingerol, although compositions varied markedly amongst the flower parts. P. maliformis flowers were open for less than one day, and the amounts of some of the compounds decreased throughout the day. The attraction of male B. jarvisi to P. maliformis flowers is most readily explained by the presence of zingerone in these flowers
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