603 research outputs found
Ramsey-like measurement of the decoherence rate between Zeeman sub-levels
Two-photon processes that involve different sub-levels of the ground state of
an atom, are highly sensitive to depopulation and decoherence within the ground
state. For example, the spectral width of electromagnetically induced
transparency resonances in type system, are strongly affected by the
ground state depopulation and decoherence rates. We present a direct
measurement of decay rates between hyperfine and Zeeman sub-levels in the
ground state of Rb vapor. Similar to the relaxation-in-the-dark
technique, pumping lasers are used to pre-align the atomic vapor in a well
defined quantum state. The free propagation of the atomic state is monitored
using a Ramsey-like method. Coherence times in the range 1-10 ms were measured
for room temperature atomic vapor. In the range of the experimental parameters
used in this study, the dominant process inducing Zeeman decoherence is the
spin-exchange collisions between rubidium atoms.Comment: 7 pages, 7 figure
The SED Machine: a robotic spectrograph for fast transient classification
Current time domain facilities are finding several hundreds of transient
astronomical events a year. The discovery rate is expected to increase in the
future as soon as new surveys such as the Zwicky Transient Facility (ZTF) and
the Large Synoptic Sky Survey (LSST) come on line. At the present time, the
rate at which transients are classified is approximately one order or magnitude
lower than the discovery rate, leading to an increasing "follow-up drought".
Existing telescopes with moderate aperture can help address this deficit when
equipped with spectrographs optimized for spectral classification. Here, we
provide an overview of the design, operations and first results of the Spectral
Energy Distribution Machine (SEDM), operating on the Palomar 60-inch telescope
(P60). The instrument is optimized for classification and high observing
efficiency. It combines a low-resolution (R100) integral field unit (IFU)
spectrograph with "Rainbow Camera" (RC), a multi-band field acquisition camera
which also serves as multi-band (ugri) photometer. The SEDM was commissioned
during the operation of the intermediate Palomar Transient Factory (iPTF) and
has already proved lived up to its promise. The success of the SEDM
demonstrates the value of spectrographs optimized to spectral classification.
Introduction of similar spectrographs on existing telescopes will help
alleviate the follow-up drought and thereby accelerate the rate of discoveries.Comment: 21 pages, 20 figure
Sleeping out-of-home in a kibbutz communal arrangement: It makes a difference for infant-mother attachment
Wetensch. publicatieFaculteit der Sociale Wetenschappe
"Children of the Dream"Revisited: 70 Years of Collective Early Child Care in Israeli Kibbutzim
FSW - Gezinsopvoeding - Ou
Simulation of semi-arid biomass plantations and irrigation using the WRF-NOAH model – a comparison with observations from Israel
A 10 × 10 km irrigated biomass plantation was simulated in an arid
region of Israel to simulate diurnal energy balances during the summer of
2012 (JJA). The goal is to examine daytime horizontal flux gradients between
plantation and desert. Simulations were carried out within the coupled
WRF-NOAH atmosphere/land surface model. MODIS land surface data was adjusted
by prescribing tailored land surface and soil/plant parameters, and by
adding a controllable sub-surface irrigation scheme to NOAH. Two model cases
studies were compared – Impact and Control. Impact simulates the irrigated plantation.
Control simulates the existing land surface, where the predominant land surface is
bare desert soil. Central to the study is parameter validation against land
surface observations from a desert site and from a 400 ha Simmondsia chinensis (jojoba)
plantation. Control was validated with desert observations, and Impact with Jojoba
observations. Model evapotranspiration was validated with two
Penman–Monteith estimates based on the observations.
Control simulates daytime desert conditions with a maximum deviation for surface 2 m air temperatures (T2)
of 0.2 °C, vapour pressure deficit (VPD) of 0.25 hPa, wind
speed (U) of 0.5 m s−1, surface radiation (Rn) of 25 W m−2,
soil heat flux (G) of 30 W m−2 and 5 cm soil temperatures (ST5) of
1.5 °C. Impact simulates irrigated vegetation conditions with a maximum deviation for T2 of 1–1.5 °C,
VPD of 0.5 hPa, U of 0.5 m s−1, Rn of 50 W m−5,
G of 40 W m−2 and ST5 of 2 °C.
Latent heat curves in Impact correspond closely with Penman–Monteith estimates,
and magnitudes of 160 W m−2 over the plantation are usual. Sensible heat
fluxes, are around 450 W m−2 and are at least 100–110 W m−2
higher than the surrounding desert. This surplus is driven by reduced albedo
and high surface resistance, and demonstrates that high evaporation rates
may not occur over Jojoba if irrigation is optimized. Furthermore, increased
daytime T2 over plantations highlight the need for hourly as well as daily
mean statistics. Daily mean statistics alone may imply an overall cooling
effect due to surplus nocturnal cooling, when in fact a daytime warming
effect is observed
Precursors prior to Type IIn supernova explosions are common: precursor rates, properties, and correlations
There is a growing number of supernovae (SNe), mainly of Type IIn, which
present an outburst prior to their presumably final explosion. These precursors
may affect the SN display, and are likely related to some poorly charted
phenomena in the final stages of stellar evolution. Here we present a sample of
16 SNe IIn for which we have Palomar Transient Factory (PTF) observations
obtained prior to the SN explosion. By coadding these images taken prior to the
explosion in time bins, we search for precursor events. We find five Type IIn
SNe that likely have at least one possible precursor event, three of which are
reported here for the first time. For each SN we calculate the control time.
Based on this analysis we find that precursor events among SNe IIn are common:
at the one-sided 99% confidence level, more than 50% of SNe IIn have at least
one pre-explosion outburst that is brighter than absolute magnitude -14, taking
place up to 1/3 yr prior to the SN explosion. The average rate of such
precursor events during the year prior to the SN explosion is likely larger
than one per year, and fainter precursors are possibly even more common. We
also find possible correlations between the integrated luminosity of the
precursor, and the SN total radiated energy, peak luminosity, and rise time.
These correlations are expected if the precursors are mass-ejection events, and
the early-time light curve of these SNe is powered by interaction of the SN
shock and ejecta with optically thick circumstellar material.Comment: 15 pages, 20 figures, submitted to Ap
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