324 research outputs found
Finite-size effects in tunneling between parallel quantum wires
We present theoretical calculations and experimental measurements which
reveal finite-size effects in the tunneling between two parallel quantum wires,
fabricated at the cleaved edge of a GaAs/AlGaAs bilayer heterostructure.
Observed oscillations in the differential conductance, as a function of bias
voltage and applied magnetic field, provide direct information on the shape of
the confining potential. Superimposed modulations indicate the existence of two
distinct excitation velocities, as expected from spin-charge separation.Comment: Accepted to Phys. Rev. Lett. 7/200
FGF Signaling Regulates the Number of Posterior Taste Papillae by Controlling Progenitor Field Size
The sense of taste is fundamental to our ability to ingest nutritious substances and to detect and avoid potentially toxic ones. Sensory taste buds are housed in papillae that develop from epithelial placodes. Three distinct types of gustatory papillae reside on the rodent tongue: small fungiform papillae are found in the anterior tongue, whereas the posterior tongue contains the larger foliate papillae and a single midline circumvallate papilla (CVP). Despite the great variation in the number of CVPs in mammals, its importance in taste function, and its status as the largest of the taste papillae, very little is known about the development of this structure. Here, we report that a balance between Sprouty (Spry) genes and Fgf10, which respectively antagonize and activate receptor tyrosine kinase (RTK) signaling, regulates the number of CVPs. Deletion of Spry2 alone resulted in duplication of the CVP as a result of an increase in the size of the placode progenitor field, and Spry1−/−;Spry2−/− embryos had multiple CVPs, demonstrating the redundancy of Sprouty genes in regulating the progenitor field size. By contrast, deletion of Fgf10 led to absence of the CVP, identifying FGF10 as the first inductive, mesenchyme-derived factor for taste papillae. Our results provide the first demonstration of the role of epithelial-mesenchymal FGF signaling in taste papilla development, indicate that regulation of the progenitor field size by FGF signaling is a critical determinant of papilla number, and suggest that the great variation in CVP number among mammalian species may be linked to levels of signaling by the FGF pathway
Interference and zero-bias anomaly in tunneling between Luttinger-liquid wires
We present theoretical calculations and experimental measurements which
reveal the Luttinger-liquid (LL) nature of elementary excitations in a system
consisting of two quantum wires connected by a long narrow tunnel junction at
the edge of a GaAs/AlGaAs bilayer heterostructure. The boundaries of the wires
are important and lead to a characteristic interference pattern in measurements
on short junctions. We show that the experimentally observed modulation of the
conductance oscillation amplitude as a function of the voltage bias can be
accounted for by spin-charge separation of the elementary excitations in the
interacting wires. Furthermore, boundaries affect the LL exponents of the
voltage and temperature dependence of the tunneling conductance at low
energies. We show that the measured temperature dependence of the conductance
zero-bias dip as well as the voltage modulation of the conductance oscillation
pattern can be used to extract the electron interaction parameters in the
wires.Comment: 17 pages, 12 figure
Many-body dispersions in interacting ballistic quantum wires
We have measured the collective excitation spectrum of interacting electrons
in one-dimension. The experiment consists of controlling the energy and
momentum of electrons tunneling between two clean and closely situated,
parallel quantum wires in a GaAs/AlGaAs heterostructure while measuring the
resulting conductance. We measure excitation spectra that clearly deviate from
the non-interacting spectrum, attesting to the importance of Coulomb
interactions. Notable is an observed 30% enhancement of the velocity of the
main excitation branch relative to non-interacting electrons with the same
density. In short wires, finite size effects resulting from broken
translational invariance are observed. Spin - charge separation is manifested
through moire patterns, reflecting different spin and charge excitation
velocities.Comment: 14 pages, 6 eps figures. To be published in NANOWIRE, a special issue
of Solid State Communication
The Quantum-Classical Crossover in the Adiabatic Response of Chaotic Systems
The autocorrelation function of the force acting on a slow classical system,
resulting from interaction with a fast quantum system is calculated following
Berry-Robbins and Jarzynski within the leading order correction to the
adiabatic approximation. The time integral of the autocorrelation function is
proportional to the rate of dissipation. The fast quantum system is assumed to
be chaotic in the classical limit for each configuration of the slow system. An
analytic formula is obtained for the finite time integral of the correlation
function, in the framework of random matrix theory (RMT), for a specific
dependence on the adiabatically varying parameter. Extension to a wider class
of RMT models is discussed. For the Gaussian unitary and symplectic ensembles
for long times the time integral of the correlation function vanishes or falls
off as a Gaussian with a characteristic time that is proportional to the
Heisenberg time, depending on the details of the model. The fall off is
inversely proportional to time for the Gaussian orthogonal ensemble. The
correlation function is found to be dominated by the nearest neighbor level
spacings. It was calculated for a variety of nearest neighbor level spacing
distributions, including ones that do not originate from RMT ensembles. The
various approximate formulas obtained are tested numerically in RMT. The
results shed light on the quantum to classical crossover for chaotic systems.
The implications on the possibility to experimentally observe deterministic
friction are discussed.Comment: 26 pages, including 6 figure
Hypoxia as a therapy for mitochondrial disease
Defects in the mitochondrial respiratory chain (RC) underlie a spectrum of human conditions, ranging from devastating inborn errors of metabolism to aging. We performed a genome-wide Cas9-mediated screen to identify factors that are protective during RC inhibition. Our results highlight the hypoxia response, an endogenous program evolved to adapt to limited oxygen availability. Genetic or small-molecule activation of the hypoxia response is protective against mitochondrial toxicity in cultured cells and zebrafish models. Chronic hypoxia leads to a marked improvement in survival, body weight, body temperature, behavior, neuropathology, and disease biomarkers in a genetic mouse model of Leigh syndrome, the most common pediatric manifestation of mitochondrial disease. Further preclinical studies are required to assess whether hypoxic exposure can be developed into a safe and effective treatment for human diseases associated with mitochondrial dysfunction.National Institute of Mental Health (U.S.) (Grant 5DP1-MH100706)National Institute of Mental Health (U.S.) (Grant 1R01-MH110049)National Institute of Neurological Diseases and Stroke (U.S.) (Grant 5R01DK097768-03
A dominant negative mutation uncovers cooperative control of caudal Wolffian duct development by Sprouty genes
The Wolffian ducts (WD) are paired epithelial tubules central to the development of the mammalian genitourinary tract. Outgrowths from the WD known as the ureteric buds (UB) generate the collecting ducts of the kidney. Later during development, the caudal portion of the WD will form the vas deferens, epididymis and seminal vesicle in males, and will degenerate in females. While the genetic pathways controlling the development of the UB are firmly established, less is known about those governing development of WD portions caudal to the UB. Sprouty proteins are inhibitors of receptor tyrosine kinase (RTK) signaling in vivo. We have recently shown that homozygous mutation of a conserved tyrosine (Tyr53) of Spry1 results in UB defects indistinguishable from that of Spry1 null mice. Here, we show that heterozygosity for the Spry1 Y53A allele causes caudal WD developmental defects consisting of ectopically branched seminal vesicles in males and persistent WD in females, without affecting kidney development. Detailed analysis reveals that this phenotype also occurs in Spry1+/- mice but with a much lower penetrance, indicating that removal of tyrosine 53 generates a dominant negative mutation in vivo. Supporting this notion, concomitant deletion of one allele of Spry1 and Spry2 also recapitulates the genital phenotype of Spry1Y53A/+ mice with high penetrance. Mechanistically, we show that unlike the effects of Spry1 in kidney development, these caudal WD defects are independent of Ret signaling, but can be completely rescued by lowering the genetic dosage of Fgf10. In conclusion, mutation of tyrosine 53 of Spry1 generates a dominant negative allele that uncovers fine-tuning of caudal WD development by Sprouty genes.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This work was supported by grants BFU2017-83646-P (MINECO) and PID2020-114947 GB-I00 (MCIU) (both supported by funds from AEI/FEDER, UE) to ME. MV was supported by a predoctoral fellowship from AGAUR. GA and CA and GA are supported by a fellowship from Universitat de Lleida. SC was supported by a Cofund action from the Marie Curie program of the E
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