1,593 research outputs found
Optical Self Energy in Graphene due to Correlations
In highly correlated systems one can define an optical self energy in analogy
to its quasiparticle (QP) self energy counterpart. This quantity provides
useful information on the nature of the excitations involved in inelastic
scattering processes. Here we calculate the self energy of the intraband
optical transitions in graphene originating in the electron-electron
interaction (EEI) as well as electron-phonon interaction (EPI). Although optics
involves an average over all momenta () of the charge carriers, the
structure in the optical self energy is nevertheless found to mirror mainly
that of the corresponding quasiparticles for equal to or near the Fermi
momentum . Consequently plasmaronic structures which are associated with
momenta near the Dirac point at are not important in the intraband
optical response. While the structure of the electron-phonon interaction (EPI)
reflects the sharp peaks of the phonon density of states, the excitation
spectrum associated with the electron-electron interaction is in comparison
structureless and flat and extends over an energy range which scales linearly
with the value of the chemical potential. Modulations seen on the edge of the
interband optical conductivity as it rises towards its universal background
value are traced to structure in the quasiparticle self energies around
of the lower Dirac cone associated with the occupied states.Comment: 30 pages, 10 figure
HIFI spectroscopy of low-level water transitions in M82
We present observations of the rotational ortho-water ground transition, the
two lowest para-water transitions, and the ground transition of ionised
ortho-water in the archetypal starburst galaxy M82, performed with the HIFI
instrument on the Herschel Space Observatory. These observations are the first
detections of the para-H2O(111-000) (1113\,GHz) and ortho-H2O+(111-000)
(1115\,GHz) lines in an extragalactic source. All three water lines show
different spectral line profiles, underlining the need for high spectral
resolution in interpreting line formation processes. Using the line shape of
the para-H2O(111-000) and ortho-H2O+(111-000) absorption profile in conjunction
with high spatial resolution CO observations, we show that the (ionised) water
absorption arises from a ~2000 pc^2 region within the HIFI beam located about
~50 pc east of the dynamical centre of the galaxy. This region does not
coincide with any of the known line emission peaks that have been identified in
other molecular tracers, with the exception of HCO. Our data suggest that water
and ionised water within this region have high (up to 75%) area-covering
factors of the underlying continuum. This indicates that water is not
associated with small, dense cores within the ISM of M82 but arises from a more
widespread diffuse gas component.Comment: 5 pages, 4 figures. Accepted for publication in A&
A valley-spin qubit in a carbon nanotube
Although electron spins in III-V semiconductor quantum dots have shown great
promise as qubits, a major challenge is the unavoidable hyperfine decoherence
in these materials. In group IV semiconductors, the dominant nuclear species
are spinless, allowing for qubit coherence times that have been extended up to
seconds in diamond and silicon. Carbon nanotubes are a particularly attractive
host material, because the spin-orbit interaction with the valley degree of
freedom allows for electrical manipulation of the qubit. In this work, we
realise such a qubit in a nanotube double quantum dot. The qubit is encoded in
two valley-spin states, with coherent manipulation via electrically driven spin
resonance (EDSR) mediated by a bend in the nanotube. Readout is performed by
measuring the current in Pauli blockade. Arbitrary qubit rotations are
demonstrated, and the coherence time is measured via Hahn echo. Although the
measured decoherence time is only 65 ns in our current device, this work offers
the possibility of creating a qubit for which hyperfine interaction can be
virtually eliminated
HIFI spectroscopy of low-level water transitions in M82
We present observations of the rotational ortho-water ground transition, the
two lowest para-water transitions, and the ground transition of ionised
ortho-water in the archetypal starburst galaxy M82, performed with the HIFI
instrument on the Herschel Space Observatory. These observations are the first
detections of the para-H2O(111-000) (1113\,GHz) and ortho-H2O+(111-000)
(1115\,GHz) lines in an extragalactic source. All three water lines show
different spectral line profiles, underlining the need for high spectral
resolution in interpreting line formation processes. Using the line shape of
the para-H2O(111-000) and ortho-H2O+(111-000) absorption profile in conjunction
with high spatial resolution CO observations, we show that the (ionised) water
absorption arises from a ~2000 pc^2 region within the HIFI beam located about
~50 pc east of the dynamical centre of the galaxy. This region does not
coincide with any of the known line emission peaks that have been identified in
other molecular tracers, with the exception of HCO. Our data suggest that water
and ionised water within this region have high (up to 75%) area-covering
factors of the underlying continuum. This indicates that water is not
associated with small, dense cores within the ISM of M82 but arises from a more
widespread diffuse gas component.Comment: 5 pages, 4 figures. Accepted for publication in A&
The release of dissolved actinium to the ocean : A global comparison of different end-members
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 109 (2008): 409-420, doi:10.1016/j.marchem.2007.07.005.The measurement of short-lived 223Ra often involves a second measurement for supported
activities, which represents 227Ac in the sample. Here we exploit this fact, presenting a set of
284 values on the oceanic distribution of 227Ac, which was collected when analyzing water
samples for short-lived radium isotopes by the radium delayed coincidence counting system.
The present work compiles 227Ac data from coastal regions all over the northern hemisphere,
including values from ground water, from estuaries and lagoons, and from marine endmembers.
Deep-sea samples from a continental slope off Puerto Rico and from an active
vent site near Hawaii complete the overview of 227Ac near its potential sources.
The average 227Ac activities of nearshore marine end-members range from 0.4 dpm * m-3 at
the Gulf of Mexico to 3.0 dpm *m-3 in the coastal waters of the Korean Strait. In analogy to
228Ra, we find the extension of adjacent shelf regions to play a substantial role for 227Ac
activities, although less pronounced than for radium, due to its weaker shelf source. Based
on previously published values, we calculate an open ocean 227Ac inventory of 1.35 *
1018 dpm 227Acex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux
of 127 dpm*m-2*y-1 from the deep-sea floor. For the shelf regions, we obtain a global
inventory of 227Ac of 4.5 * 1015 dpm, which cannot be converted directly into a flux value, as
the regional loss term of 227Ac to the open ocean would have to be included.
Ac has so far been considered to behave similarly to Ra in the marine environment, with the
exception of a strong Ac source in the deep-sea due to 231Paex. Here, we present evidence of
geochemical differences between Ac, which is retained in a warm vent system, and Ra,
which is readily released (Moore et al., submitted). Another potential mechanism of
producing deviations in 227Ac/228Ra and daughter isotope ratios from the expected production
value of lithogenic material is observed at reducing environments, where enrichment in
uranium may occur. The presented data here may serve as a reference for including 227Ac in
circulation models, and the overview provides values for some end-members that contribute
to the global Ac distribution
CHESS, Chemical Herschel surveys of star forming regions:Peering into the protostellar shock L1157-B1
The outflow driven by the low-mass class 0 protostar L1157 is the prototype
of the so-called chemically active outflows. The bright bowshock B1 in the
southern outflow lobe is a privileged testbed of magneto-hydrodynamical (MHD)
shock models, for which dynamical and chemical processes are strongly
interdependent. We present the first results of the unbiased spectral survey of
the L1157-B1 bowshock, obtained in the framework of the key program "Chemical
Herschel Surveys of Star Forming Regions" (CHESS). The main aim is to trace the
warm and chemically enriched gas and to infer the excitation conditions in the
shock region. The CO 5-4 and H2O lines have been detected at high-spectral
resolution in the unbiased spectral survey of the HIFI-Band 1b spectral window
(555-636 GHz), presented by Codella et al. in this volume. Complementary
ground-based observations in the submm window help establish the origin of the
emission detected in the main-beam of HIFI, and the physical conditions in the
shock.}{Both lines exhibit broad wings, which extend to velocities much higher
than reported up to now. We find that the molecular emission arises from two
regions with distinct physical conditions: an extended, warm (100K), dense (3e5
cm-3) component at low-velocity, which dominates the water line flux in Band~1;
a secondary component in a small region of B1 (a few arcsec) associated with
high-velocity, hot (> 400 K) gas of moderate density ((1.0-3.0)e4 cm-3), which
appears to dominate the flux of the water line at 179mu observed with PACS. The
water abundance is enhanced by two orders of magnitude between the low- and the
high-velocity component, from 8e-7 up to 8e-5. The properties of the
high-velocity component agree well with the predictions of steady-state C-shock
models.Comment: Accepted for Publication in Astronomy and Astrophysics (Herschel
Special Issue
White Paper: Open Digital Health – accelerating transparent and scalable health promotion and treatment
In this White Paper, we outline recommendations from the perspective of health psychology and behavioural science, addressing three research gaps: (1) What methods in the health psychology research toolkit can be best used for developing and evaluating digital health tools? (2) What are the most feasible strategies to reuse digital health tools across populations and settings? (3) What are the main advantages and challenges of sharing (openly publishing) data, code, intervention content and design features of digital health tools? We provide actionable suggestions for researchers joining the continuously growing Open Digital Health movement, poised to revolutionise health psychology research and practice in the coming years. This White Paper is positioned in the current context of the COVID-19 pandemic, exploring how digital health tools have rapidly gained popularity in 2020-2022, when world-wide health promotion and treatment efforts rapidly shifted from face-to-face to remote delivery. This statement is written by the Directors of the not-for-profit Open Digital Health initiative (n = 6), Experts attending the European Health Psychology Society Synergy Expert Meeting (n = 17), and the initiative consultant, following a two-day meeting (19-20th August 2021).Peer reviewe
White Paper: Open Digital Health – accelerating transparent and scalable health promotion and treatment
Recovery after critical illness: putting the puzzle together-a consensus of 29.
In this review, we seek to highlight how critical illness and critical care affect longer-term outcomes, to underline the contribution of ICU delirium to cognitive dysfunction several months after ICU discharge, to give new insights into ICU acquired weakness, to emphasize the importance of value-based healthcare, and to delineate the elements of family-centered care. This consensus of 29 also provides a perspective and a research agenda about post-ICU recovery
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