Bose-Einstein Condensation in Microgravity van Zoest, T; Gaaloul, N; Singh, Y ...
Science (American Association for the Advancement of Science),
06/2010, Letnik:
328, Številka:
5985
Journal Article
Recenzirano
Albert Einstein's insight that it is impossible to distinguish a local experiment in a "freely falling elevator" from one in free space led to the development of the theory of general relativity. The ...wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.
The Largest M Dwarf Flares from ASAS-SN Schmidt, Sarah J.; Shappee, Benjamin J.; van Saders, Jennifer L. ...
Astrophysical journal/The Astrophysical journal,
05/2019, Letnik:
876, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The All-sky Automated Survey for Supernovae (ASAS-SN) is the only project in existence to scan the entire sky in optical light approximately every day, reaching a depth of g ∼ 18 mag. Over the course ...of its first 4 yr of transient alerts (2013-2016), ASAS-SN observed 53 events classified as likely M dwarf flares. We present follow-up photometry and spectroscopy of all 53 candidates, confirming flare events on 47 M dwarfs, one K dwarf, and one L dwarf. The remaining four objects include a previously identified T Tauri star, a young star with outbursts, and two objects too faint to confirm. A detailed examination of the 49 flare star light curves revealed an additional six flares on five stars, resulting in a total of 55 flares on 49 objects ranging in V-band contrast from ΔV = −1 to −10.2 mag. Using an empirical flare model to estimate the unobserved portions of the flare light curve, we obtain lower limits on the V-band energy emitted during each flare, spanning -35, which are among the most energetic flares detected on M dwarfs. The ASAS-SN M dwarf flare stars show a higher fraction of H emission, as well as stronger H emission, compared to M dwarfs selected without reference to activity, consistent with belonging to a population of more magnetically active stars. We also examined the distribution of tangential velocities, finding that the ASAS-SN flaring M dwarfs are likely to be members of the thin disk and are neither particularly young nor old.
Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Because of their unique coherence properties, Bose-Einstein condensates ...are ideal sources for an atom interferometer in extended free fall. In this Letter we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far field of a double slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.
Electrochromes are materials that have the ability to reversibly change from one colour state to another with the application of an electric field. Electrochromic colouration efficiency is typically ...large in organic materials that are not very stable chemically. Here we show that inorganic Bi(0.9)Ca(0.1)FeO(3-0.05) thin films exhibit a prominent electrochromic effect arising from an intrinsic mechanism due to the melting of oxygen-vacancy ordering and the associated redistribution of carriers. We use a combination of optical characterization techniques in conjunction with high-resolution transmission electron microscopy and first-principles theory. The absorption change and colouration efficiency at the band edge (blue-cyan region) are 4.8×10(6) m(-1) and 190 cm(2) C(-1), respectively, which are the highest reported values for inorganic electrochromes, even exceeding values of some organic materials.
Recent advances have enabled organotypic culture of beating human myocardial slices that are stable for weeks. However, human myocardial samples are rare, exhibit high variability and frequently ...originate from diseased hearts. Thus, there is a need to adapt long-term slice culture for animal myocardium. When applied to animal cardiac slices, studies in healthy or genetically modified myocardium will be possible. We present the culture of slices from rabbit hearts, which resemble the human heart in microstructure, electrophysiology and excitation-contraction coupling.
Left ventricular myocardium from New Zealand White rabbits was cut using a vibratome and cultured in biomimetic chambers for up to 7 days (d). Electro-mechanical uncoupling agents 2,3-butanedione monoxime (BDM) and cytochalasin D (CytoD) were added during initiation of culture and effects on myocyte survival were quantified. We investigated pacing rates (0.5 Hz, 1 Hz, and 2 Hz) and hormonal supplements (cortisol, T3, catecholamines) at physiological plasma concentrations. T3 was buffered using BSA. Contractile force was recorded continuously. Glucose consumption and lactate production were measured. Whole-slice Ca
transients and action potentials were recorded. Effects of culture on microstructure were investigated with confocal microscopy and image analysis.
Protocols for human myocardial culture resulted in sustained contracture and myocyte death in rabbit slices within 24 h, which could be prevented by transient application of a combination of BDM and CytoD. Cortisol stabilized contraction amplitude and kinetics in culture. T3 and catecholaminergic stimulation did not further improve stability. T3 and higher pacing rates increased metabolic rate and lactate production. T3 stabilized the response to β-adrenergic stimulation over 7 d. Pacing rates above 1 Hz resulted in progredient decline in contraction force. Image analysis revealed no changes in volume fractions of cardiomyocytes or measures of fibrosis over 7 d. Ca
transient amplitudes and responsiveness to isoprenaline were comparable after 1 d and 7 d, while Ca
transient duration was prolonged after 7 d in culture.
A workflow for rabbit myocardial culture has been established, preserving function for up to 7 d. This research underscores the importance of glucocorticoid signaling in maintaining tissue function and extending culture duration. Furthermore, BDM and CytoD appear to protect from tissue damage during the initiation phase of tissue culture.
The paper describes a geometrical optics based model to predict propagation within buildings for personal communication system (PCS) design. A ray tracing model for predicting propagation based on a ...building blueprint representation is presented for a transmitter and receiver located on the same floor inside a building. Measured and predicted propagation data are presented as power delay profiles that contain the amplitude and arrival time of individual multipath components. Measured and predicted power delay profiles are compared on a location-by-location basis to provide both a qualitative and a quantitative measure of the model accuracy. The concept of effective building material properties is developed, and the effective building material properties are derived for two dissimilar buildings based upon comparison of measured and predicted power delay profiles. Time delay comparison shows that the amplitudes of many significant multipath components are accurately predicted by this model. Path loss between a transmitter and receiver is predicted with a standard deviation of less than 5 dB over 45 locations in two different buildings.< >
We perform a strong lensing analysis of the merging galaxy cluster MACS J0416.1?2403 (M0416; z = 0.42) in recent CLASH/HST observations. We identify 70 new multiple images and candidates of 23 ...background sources in the range 0.7 <, ~ z sub(phot) <, ~ 6.14 including two probable high-redshift dropouts, revealing a highly elongated lens with axis ratio Asymptotically = to25:1, and a major axis of ~100" (z sub(s) ~ 2). Compared to other well-studied clusters, M0416 shows an enhanced lensing efficiency. Although the critical area is not particularly large (Asymptotically = to0.6 whitesquare'; z sub(s) ~ 2), the number of multiple images, per critical area, is anomalously high. We calculate that the observed elongation boosts the number of multiple images, per critical area, by a factor of ~2.5x, due to the increased ratio of the caustic area relative to the critical area. Additionally, we find that the observed separation between the two main mass components enlarges the critical area by a factor of ~2. These geometrical effects can account for the high number (density) of multiple images observed. We find in numerical simulations that only ~4% of the clusters (with M sub(vir) > or =, slanted 6 x 10 super(14) h super(-1) M sub(middle in circle)) exhibit critical curves as elongated as in M0416.
Qualitative models are presented that predict the effects of walls, office partitions, floors, and building layout on the path loss at 914 MHz. The site-specific models have been developed based on ...the number of floors, partitions, and concrete walls between the transmitter and receiver, and provide simple prediction rules which relate signal strength to the log of distance. The standard deviation between measured and predicted path loss is 5.8 dB for the entire data set, and can be as small as 4 dB for specific areas within a building. Average floor attenuation factors, which describe the additional path loss (in decibels) caused by floors between transmitter and receiver, are found for as many as four floors in a typical office building. Path loss contour plots for measured data are presented. In addition, contour plots for the path loss prediction error indicate that the prediction models presented are accurate to within 6 dB for a majority of locations in a building.< >
Using the detector ARGUS at the
e
+
e
− storage ring DORIS II at DESY, we have observed the decays
Λ
c
+ →
Ξ
−
K
+
π
+ and
Λ
c
+ → Ξ
∗0K
+
and obtained evidence for the decay
Ξ
c
0 →
ΛK
s
0. All ...three of these decays are of interest as they provide information about
W-exchange processes. The products of cross sections and branching ratios for
Λ
c
+ →
Ξ
−
K
+
π
+ and
Λ
c
+ → Ξ
∗0K
+
are (1.7±0.3±0.3) pb and (0.6±0.2±0.1) pb, respectively, which implies that (35±17) % of the
Ξ
−
K
+
π
+ final state is generated through a two-body decay via intermediate
W-exchange. The product of production cross section and branching ratio for
Ξ
c
0 →
Λ
K
s
0 is (2.1 ± 1.0 ± 0.6) pb.
PDF
