772 research outputs found
Tuning Rashba and Dresselhaus spin-orbit couplings: Effects on singlet and triplet condensation with Fermi atoms
We investigate the pair condensation of a two-spin-component Fermi gas in the
presence of both Rashba and Dresselhaus spin-orbit couplings. We calculate the
condensate fraction in the BCS-BEC crossover both in two and in three
dimensions by taking into account singlet and triplet pairings. These
quantities are studied by varying the spin-orbit interaction from the case with
the only Rashba to the equal-Rashba-Dresselhaus one. We find that, by mixing
the two couplings, the singlet pairing decreases while the triplet pairing is
suppressed in the BCS regime and increased in the BEC regime, both in two and
three dimensions. At fixed spin-orbital strength, the greatest total condensate
fraction is obtained when only one coupling (only Rashba or only Dresselhaus)
is present.Comment: 9 pages, 6 figures, final versio
Life and being. The twofold beginning of heidegger’s seinsfrage
Heidegger has always stated that the distinctive feature of his ontology is the question of Being. But actually, the question with which Heidegger faces philosophy is by no means addressed to Being. It is addressed to “life”, i.e. to the connection, in life, of existence and history as a “living spirit”. It is this question that holds back the mature question on the being from resolving itself in a pure speculative scholasticism on Being and its history. It is this question that fecundates with the question of being the philosophically important nucleus: existential analytics; dialogue with poetry and the work of art; the great question about technique. In the thought that looks into Being in its character as an event, the theme that remains alive is that Being for us is ultimately the world we inhabit
Synthetic Methods Driven by the Photoactivity of Electron Donor-Acceptor Complexes
The association of an electron-rich substrate with an electron-accepting molecule can generate a new molecular aggregate in the ground state, called an electron donor-acceptor (EDA) complex. Even when the two precursors do not absorb visible light, the resulting EDA complex often does. In 1952, Mulliken proposed a quantum-mechanical theory to rationalize the formation of such colored EDA complexes. However, and besides a few pioneering studies in the 20th century, it is only in the past few years that the EDA complex photochemistry has been recognized as a powerful strategy for expanding the potential of visible-light-driven radical synthetic chemistry. Here, we explain why this photochemical synthetic approach was overlooked for so long. We critically discuss the historical context, scientific reasons, serendipitous observations, and landmark discoveries that were essential for progress in the field. We also outline future directions and identify the key advances that are needed to fully exploit the potential of the EDA complex photochemistry
Radio continuum properties of luminous infrared galaxies. Identifying the presence of an AGN in the radio
Luminous infrared galaxies are systems enshrouded in dust, which absorbs most
of their optical/UV emission and re-radiates it in the mid- and far-infrared.
Radio observations are largely unaffected by dust obscuration, enabling us to
study the central regions of LIRGs in an unbiased manner. The main goal of this
project is to examine how the radio properties of local LIRGs relate to their
infrared spectral characteristics. Here we present an analysis of the radio
continuum properties of a subset of the Great Observatories All-sky LIRG Survey
(GOALS), which consists of 202 nearby systems (z<0.088). Our radio sample
consists of 35 systems, or 46 individual galaxies, that were observed at both
1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The
aim of the project is to use the radio imagery to probe the central kpc of
these LIRGs in search of active galactic nuclei. We used the archival data at
1.49 and 8.44 GHz to create radio-spectral-index maps using the standard
relation between flux density Sv and frequency v, S~v^-a, where a is the radio
spectral index. By studying the spatial variations in a, we classified the
objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the
presence of an active nucleus using the radio morphology, deviations from the
radio/infrared correlation, and spatially resolved spectral index maps, and
then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII]
line ratios and EQW of the 6.2 um PAH feature) and optical (BPT diagram) AGN
diagnostics. We find that 21 out of the 46 objects in our sample are radio-AGN,
9 are classified as starbursts (SB), and 16 are AGN/SB. After comparing to
other AGN diagnostics we find 3 objects out of the 46 that are identified as
AGN based on the radio analysis, but are not classified as such based on the
mid-infrared and optical AGN diagnostics presented in this study.Comment: 33 pages, 7 figures, 5 tables, to appear in A&
Catalytic asymmetric C–C cross-couplings enabled by photoexcitation
Enantioselective catalytic processes are promoted by chiral catalysts that can execute a specific mode of catalytic reactivity, channeling the chemical reaction through a certain mechanistic pathway. Here, we show how by simply using visible light we can divert the established ionic reactivity of a chiral allyl–iridium(iii) complex to switch on completely new catalytic functions, enabling mechanistically unrelated radical-based enantioselective pathways. Photoexcitation provides the chiral organometallic intermediate with the ability to activate substrates via an electron-transfer manifold. This redox event unlocks an otherwise inaccessible cross-coupling mechanism, since the resulting iridium(ii) centre can intercept the generated radicals and undergo a reductive elimination to forge a stereogenic centre with high stereoselectivity. This photochemical strategy enables difficult-to-realize enantioselective alkyl–alkyl cross-coupling reactions between allylic alcohols and readily available radical precursors, which are not achievable under thermal activation. [Figure not available: see fulltext.
Zero Sound and First Sound in a Disk-Shaped Normal Fermi gas
We study the zero sound and the first sound in a dilute and ultracold
disk-shaped normal Fermi gas with a strong harmonic confinement along the axial
direction and uniform in the two planar directions. Working at zero temperature
we calculate the chemical potential of the fermionic fluid as a function
of the uniform planar density and find that changes its slope in
correspondence to the filling of harmonic axial modes (shell effects). Within
the linear response theory, and under the random phase approximation, we
calculate the velocity of the zero sound. We find that also
changes its slope in correspondence of the filling of the harmonic axial modes
and that this effect depends on the Fermi-Fermi scattering length . In the
collisional regime, we calculate the velocity of first sound showing that
displays jumps at critical densities fixed by the scattering length
. Finally, we discuss the experimental achievability of these zero sound
and first sound waves with ultracold alkali-metal atoms.Comment: 9 pages, 5 figures, editorially approved for publication on Phys.
Rev.
The endocannabinoid 2-AG controls skeletal muscle cell differentiation via CB1 receptor-dependent inhibition of Kv7 channels.
Little is known of the involvement of endocannabinoids and cannabinoid receptors in skeletal muscle cell differentiation. We report that, due to changes in the expression of genes involved in its metabolism, the levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) are decreased both during myotube formation in vitro from murine C2C12 myoblasts and during mouse muscle growth in vivo. The endocannabinoid, as well as the CB1 agonist arachidonoyl-2-chloroethylamide, prevent myotube formation in a manner antagonized by CB1 knockdown and by CB1 antagonists, which, per se, instead stimulate differentiation. Importantly, 2-AG also inhibits differentiation of primary human satellite cells. Muscle fascicles from CB1 knockout embryos contain more muscle fibers, and postnatal mice show muscle fibers of an increased diameter relative to wild-type littermates. Inhibition of Kv7.4 channel activity, which plays a permissive role in myogenesis and depends on phosphatidylinositol 4,5-bisphosphate (PIP2), underlies the effects of 2-AG. We find that CB1 stimulation reduces both total and Kv7.4-bound PIP2 levels in C2C12 cells and inhibits Kv7.4 currents in transfected CHO cells. We suggest that 2-AG is an endogenous repressor of myoblast differentiation via CB1-mediated inhibition of Kv7.4 channels
Mid-Infrared Diagnostics of LINERs
We report results from the first mid-infrared spectroscopic study of a
comprehensive sample of 33 LINERs, observed with the Spitzer Space Telescope.
We compare the properties of two different LINER populations: infrared-faint
LINERs, with LINER emission arising mostly in compact nuclear regions, and
infrared-luminous LINERs, which often show spatially extended (non-AGN) LINER
emission. We show that these two populations can be easily distinguished by
their mid-infrared spectra in three different ways: (i) their mid-IR spectral
energy distributions (SEDs), (ii) the emission features of polycyclic aromatic
hydrocarbons (PAHs), and (iii) various combinations of IR fine-structure line
ratios. IR-luminous LINERs show mid-IR SEDs typical of starburst galaxies,
while the mid-IR SEDs of IR-faint LINERs are much bluer. PAH flux ratios are
significantly different in the two groups. Fine structure emission lines from
highly excited gas, such as [O IV], are detected in both populations,
suggesting the presence of an additional AGN also in a large fraction of
IR-bright LINERs, which contributes little to the combined mid-IR light. The
two LINER groups occupy different regions of mid-infrared emission-line
excitation diagrams. The positions of the various LINER types in our diagnostic
diagrams provide important clues regarding the power source of each LINER type.
Most of these mid-infrared diagnostics can be applied at low spectral
resolution, making AGN- and starburst-excited LINERs distinguishable also at
high redshifts.Comment: 11 pages, including 2 eps figures, accepted for publication in ApJ
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