341 research outputs found
Design of Operational Transconductance Amplifiers for voltage to current conversion in gas sensing applications
This paper presents a study of Operational Transconductance Amplifiers (OTAs) for voltage to current conversion circuits. The paper includes a comparative analysis of three OTA architectures implemented in 0.35\u3bcm CMOS AMS Technology under \ub1 1.65V power supply voltage. The impact of the OTA topology has been investigated by simulation. The designed OTAs managed to deliver large current values of 10mA and 1mA to the load with a worst-case error of 0.02% under worst-case power supply and temperature conditions and a worst percentage error of 0.12% under process variation for both Miller Compensated and Capacitor Multiplier Compensated OTA. \ua9 2016 AEIT
Measurement Of The Nonlinear Ultrasonic Parameter In Aqueous Solutions
This paper deals with the measurement of the nonlinear ultrasound coefficient in aqueous solutions. Our aim is to show the possibility of using this parameter in ultrasound characterization of these solutions with the possibility of extending this technique to other complex media. The experimental determination of nonlinearity parameter is based on the quasi-linear approximation that allows us to derive an analytical expression of the second harmonic amplitude that takes into account the diffraction and the absorption effects. The experimental set up is composed of a piezoelectric disc transmitting at the fundamental frequency 2.2 MHz. The second harmonic is detected using a ring surrounding the disc and functioning at 4.4 MHz. The disc and the ring are both mounted on the same composed device and are both located in the same transversal plan to the propagation axis. The transmitted wave propagates through the sample and is detected by the receiver An appropriate signal processing permits the determination of the nonlinear parameter. The experimental results are promising and show a close correlation between the nonlinearity parameter, and the nature and the concentration of the compounds in the aqueous solutions studied.This paper deals with the measurement of the nonlinear ultrasound coefficient in aqueous solutions. Our aim is to show the possibility of using this parameter in ultrasound characterization of these solutions with the possibility of extending this technique to other complex media. The experimental determination of nonlinearity parameter is based on the quasi-linear approximation that allows us to derive an analytical expression of the second harmonic amplitude that takes into account the diffraction and the absorption effects. The experimental set up is composed of a piezoelectric disc transmitting at the fundamental frequency 2.2 MHz. The second harmonic is detected using a ring surrounding the disc and functioning at 4.4 MHz. The disc and the ring are both mounted on the same composed device and are both located in the same transversal plan to the propagation axis. The transmitted wave propagates through the sample and is detected by the receiver An appropriate signal processing permits the determination of the nonlinear parameter. The experimental results are promising and show a close correlation between the nonlinearity parameter, and the nature and the concentration of the compounds in the aqueous solutions studied
Two-dimensional superconductivity at the (111)LaAlO/SrTiO interface
We report on the discovery and transport study of the superconducting ground
state present at the (111)LaAlO/SrTiO interface. The superconducting
transition is consistent with a Berezinskii-Kosterlitz-Thouless transition and
its 2D nature is further corroborated by the anisotropy of the critical
magnetic field, as calculated by Tinkham. The estimated superconducting layer
thickness and coherence length are 10 nm and 60 nm, respectively. The results
of this work provide a new platform to clarify the microscopic details of
superconductivity at LaAlO/SrTiO interfaces, in particular in what
concerns the link with orbital symmetry.Comment: 4 pages, 4 figure
Tuning of metal-insulator transition of two-dimensional electrons at parylene/SrTiO interface by electric field
Electrostatic carrier doping using a field-effect-transistor structure is an
intriguing approach to explore electronic phases by critical control of carrier
concentration. We demonstrate the reversible control of the insulator-metal
transition (IMT) in a two dimensional (2D) electron gas at the interface of
insulating SrTiO single crystals. Superconductivity was observed in a
limited number of devices doped far beyond the IMT, which may imply the
presence of 2D metal-superconductor transition. This realization of a
two-dimensional metallic state on the most widely-used perovskite oxide is the
best manifestation of the potential of oxide electronics
Synthesis and cytotoxicity studies of Cu(I) and Ag(I) complexes based on sterically hindered β-diketonates with different degrees of fluorination
Design, synthesis, and in vitro antitumor properties of Cu(i) and Ag(i) phosphane complexes supported by the anions of sterically hindered & beta;-diketone ligands, 1,3-dimesitylpropane-1,3-dione (HLMes) and 1,3-bis(3,5-bis(trifluoromethyl)phenyl)-3-hydroxyprop-2-en-1-one (HLCF3) featuring trifluoromethyl or methyl groups on the phenyl moieties have been reported. In order to compare the biological effects of substituents on the phenyl moieties, the analogous copper(i) and silver(i) complexes of the anion of the parent 1,3-diphenylpropane-1,3-dione (HLPh) ligand were also synthesized and included in the study. In the syntheses of the Cu(i) and Ag(i) complexes, the phosphane coligands triphenylphosphine (PPh3) and 1,3,5-triaza-7-phosphaadamantane (PTA) were used to stabilize silver and copper in the +1 oxidation state, preventing the metal ion reduction to Ag(0) or oxidation to Cu(ii), respectively. X-ray crystal structures of HLCF3 and the metal adducts [Cu(L-CF3)(PPh3)(2)] and [Ag(L-Ph)(PPh3)(2)] are also presented. The antitumor properties of both classes of metal complexes were evaluated against a series of human tumor cell lines derived from different solid tumors, by means of both 2D and 3D cell viability studies. They display noteworthy antitumor properties and are more potent than cisplatin in inhibiting cancer cell growth
Spin-orbit density wave induced hidden topological order in URu2Si2
The conventional order parameters in quantum matters are often characterized
by 'spontaneous' broken symmetries. However, sometimes the broken symmetries
may blend with the invariant symmetries to lead to mysterious emergent phases.
The heavy fermion metal URu2Si2 is one such example, where the order parameter
responsible for a second-order phase transition at Th = 17.5 K has remained a
long-standing mystery. Here we propose via ab-initio calculation and effective
model that a novel spin-orbit density wave in the f-states is responsible for
the hidden-order phase in URu2Si2. The staggered spin-orbit order 'spontaneous'
breaks rotational, and translational symmetries while time-reversal symmetry
remains intact. Thus it is immune to pressure, but can be destroyed by magnetic
field even at T = 0 K, that means at a quantum critical point. We compute
topological index of the order parameter to show that the hidden order is
topologically invariant. Finally, some verifiable predictions are presented.Comment: (v2) Substantially modified from v1, more calculation and comparison
with experiments are include
Controlling magnetism with light in zero orbital angular momentum antiferromagnet
Antiferromagnetic materials feature intrinsic ultrafast spin dynamics, making them ideal candidates for future magnonic devices operating at THz frequencies. A major focus of current research is the investigation of optical methods for the efficient generation of coherent magnons in antiferromagnetic insulators. In magnetic lattices endowed with orbital angular momentum, spin-orbit coupling enables spin dynamics through the resonant excitation of low-energy electric dipoles such as phonons and orbital resonances which interact with spins. However, in magnetic systems with zero orbital angular momentum, microscopic pathways for the resonant and low-energy optical excitation of coherent spin dynamics are lacking. Here, we consider experimentally the relative merits of electronic and vibrational excitations for the optical control of zero orbital angular momentum magnets, focusing on a limit case: the antiferromagnet manganese phosphorous trisulfide (MnPS3), constituted by orbital singlet Mn2Ăľ ions. We study the correlation of spins with two types of excitations within its band gap: a bound electron orbital excitation from the singlet orbital ground state of Mn2Ăľ into an orbital triplet state, which causes coherent spin precession, and a vibrational excitation of the crystal field that causes thermal spin disorder. Our findings cast orbital transitions as key targets for magnetic control in insulators constituted by magnetic centers of zero orbital angular momentum
Ultrafast strain engineering in complex oxide heterostructures
We report on ultrafast optical experiments in which femtosecond mid-infrared
radiation is used to excite the lattice of complex oxide heterostructures. By
tuning the excitation energy to a vibrational mode of the substrate, a
long-lived five-order-of-magnitude increase of the electrical conductivity of
NdNiO3 epitaxial thin films is observed as a structural distortion propagates
across the interface. Vibrational excitation, extended here to a wide class of
heterostructures and interfaces, may be conducive to new strategies for
electronic phase control at THz repetition rates
Collapse of superconductivity in a hybrid tin-graphene Josephson junction array
When a Josephson junction array is built with hybrid
superconductor/metal/superconductor junctions, a quantum phase transition from
a superconducting to a two-dimensional (2D) metallic ground state is predicted
to happen upon increasing the junction normal state resistance. Owing to its
surface-exposed 2D electron gas and its gate-tunable charge carrier density,
graphene coupled to superconductors is the ideal platform to study the
above-mentioned transition between ground states. Here we show that decorating
graphene with a sparse and regular array of superconducting nanodisks enables
to continuously gate-tune the quantum superconductor-to-metal transition of the
Josephson junction array into a zero-temperature metallic state. The
suppression of proximity-induced superconductivity is a direct consequence of
the emergence of quantum fluctuations of the superconducting phase of the
disks. Under perpendicular magnetic field, the competition between quantum
fluctuations and disorder is responsible for the resilience at the lowest
temperatures of a superconducting glassy state that persists above the upper
critical field. Our results provide the entire phase diagram of the disorder
and magnetic field-tuned transition and unveil the fundamental impact of
quantum phase fluctuations in 2D superconducting systems.Comment: 25 pages, 6 figure
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