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781.
We present a remarkable finding that a recently discovered [G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007)10.1103/PhysRevLett.98.100504] series of pulse sequences, designed to optimally restore coherence to a qubit in the spin-boson model of decoherence, is in fact completely model independent and generically valid for arbitrary dephasing Hamiltonians given sufficiently short delay times between pulses. The series maximizes qubit fidelity versus number of applied pulses for sufficiently short delay times because the series, with each additional pulse, cancels successive orders of a time expansion for the fidelity decay. The "magical" universality of this property, which was not appreciated earlier, requires that a linearly growing set of "unknowns" (the delay times) must simultaneously satisfy an exponentially growing set of nonlinear equations that involve arbitrary dephasing Hamiltonian operators. 相似文献
782.
Time-reversal symmetry breaking by a (d+id) density-wave state in underdoped cuprate superconductors
It was proposed that the id(x(2)-y(2)) density-wave state (DDW) may be responsible for the pseudogap behavior in the underdoped cuprates. Here we show that the admixture of a small d(xy) component to the DDW state breaks the symmetry between the counterpropagating orbital currents of the DDW state and, thus, violates the macroscopic time-reversal symmetry. This symmetry breaking results in a nonzero polar Kerr effect, which has recently been observed in the pseudogap phase. 相似文献
783.
Dissociative chemisorption of methane over ruthenium, cobalt, platinum and their bimetallic counterparts supported by alumina
and NaY was investigated under a wide range of temperatures. The extent of hydrogen loss from methane was monitored by deuterium
uptake of the surface CHx species formed from methane during the course of methane chemisorption. The presence of a high average number of deuterium
in the desorbing methane suggested a widespread dissociation of methane. The initial distribution of the deuterated products
generally decreased in the sequence CD4>CHD3>CH2D2. The amount of chemisorbed methane during methane chemisorption increases with temperature and it follows the sequence of
reducibility of the supported metals and particle size which, in turn, depends on the support and the alloy formed. CHx (x=1) species prevailed on alumina supported catalysts, while on NaY supported metals, CH2 species are dominant when small metal particles are stabilized inside the supercage.
Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday 相似文献
784.
The formation of carbonaceous clusters in ion‐irradiated polymer films was investigated extensively. Information about these clusters may be obtained with ultraviolet–visible (UV–vis) spectroscopy. The optical band gap (Eg), calculated from the absorption edge of the UV spectra of these polymers, can be correlated to the number of carbon atoms (N) in a cluster with the modified Tauc equation. The structure of the cluster is also related to Eg; for example, a six‐membered‐benzene‐ring‐type structure has an Eg of ≈5.3 eV, whereas a buckminsterfullerene‐type structure has an Eg of ≈4.9 eV. These clusters are responsible for the electrical conductivity in these films. In this work, polycarbonate films (20 μm thick) were irradiated with 45‐MeV Li ions at fluences of 1 × 1012 to 1 × 1013 cm−2 and were characterized with UV–vis spectroscopy and impedance measurements. The Eg values, calculated from the absorption edge in the 280–315‐nm region with the Tauc relation, varied from 4.39 to 4.35 eV for the pristine and various irradiated samples, respectively. The cluster size showed a range of 60–62 carbon atoms per cluster. The sheet conductivity (σdc) and loss (tan δ) values of 10−16 Ω−1cm−1 and 10−3 for the pristine sample changed to 10−15 Ω−1cm−1 and 10−2, respectively, for the irradiated samples. This increase in the values of σdc and tan δ may be correlated to the increase in the size of the carbonaceous clusters. This study provides insight into the mechanism of electrical conductivity in irradiated polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1589–1594, 2000 相似文献
785.
GautamR. Desiraju JackD. Dunitz Ashwini Nangia JagarlapudiA.R.P. Sarma Engelbert Zass 《Helvetica chimica acta》2000,83(1):1-15
There are more organic compounds with an even number of carbon atoms than with an odd number. This disparity could result mainly from the methods used in synthetic chemistry to build large molecules from smaller ones. Samples of C28, C47 and C48 compounds have been examined in this context. 相似文献
786.
Two‐dimensional incompressible jet development inside a duct has been studied in the laminar flow regime, for cases with and without entrainment of ambient fluid. Results have been obtained for the flow structure and critical Reynolds number values for steady asymmetric jet development and for the onset of temporal oscillations, at various values of the duct‐to‐jet width ratio (aspect ratio). It is found that at low aspect ratios and Reynolds numbers, jet development inside the duct is symmetric. For larger aspect ratios and Reynolds numbers, the jet flow at steady state becomes asymmetric with respect to the midplane, and for still higher values, it becomes oscillatory with respect to time. When entrainment is present, the instabilities of asymmetric development and temporal oscillations occur at a much higher critical Reynolds number for a given aspect ratio, indicating that the stability of the jet flow is higher with entrainment. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
787.
Ragavesh Dhandapani Imene Mitiche Scott McMeekin Venkateswara Sarma Mallela Gordon Morison 《Entropy (Basel, Switzerland)》2021,23(12)
This paper presents a new approach for denoising Partial Discharge (PD) signals using a hybrid algorithm combining the adaptive decomposition technique with Entropy measures and Group-Sparse Total Variation (GSTV). Initially, the Empirical Mode Decomposition (EMD) technique is applied to decompose a noisy sensor data into the Intrinsic Mode Functions (IMFs), Mutual Information (MI) analysis between IMFs is carried out to set the mode length K. Then, the Variational Mode Decomposition (VMD) technique decomposes a noisy sensor data into K number of Band Limited IMFs (BLIMFs). The BLIMFs are separated as noise, noise-dominant, and signal-dominant BLIMFs by calculating the MI between BLIMFs. Eventually, the noise BLIMFs are discarded from further processing, noise-dominant BLIMFs are denoised using GSTV, and the signal BLIMFs are added to reconstruct the output signal. The regularization parameter for GSTV is automatically selected based on the values of Dispersion Entropy of the noise-dominant BLIMFs. The effectiveness of the proposed denoising method is evaluated in terms of performance metrics such as Signal-to-Noise Ratio, Root Mean Square Error, and Correlation Coefficient, which are are compared to EMD variants, and the results demonstrated that the proposed approach is able to effectively denoise the synthetic Blocks, Bumps, Doppler, Heavy Sine, PD pulses and real PD signals. 相似文献
788.
Niharika Keot Bittu Lama Haobam Kisan Singh Himangshu Pratim Bhattacharyya Dr. Manabendra Sarma 《Chemphyschem》2023,24(23):e202300413
The importance of noncovalent interaction has gained attention in various domains covering drug and novel catalyst design. The present study mainly characterizes the role of hydrogen bond (H-bond) and other intermolecular interactions in different (1 : 1) complex analogues formed between the N-aryl-thiazol-2-ylidene (YR) and five proton donor (HX) molecules. The analysis of the singlet-triplet energy gap ( ) confirmed the stability of the singlet state for this class of N-aryl-thiazol-2-ylidenes than the triplet state. The interaction energy values of the YR-HX complexes follow the order: YR-NH3<YR-HCN<YR-H2O<YR-MeOH<YR-HF. In addition, substituting the H-atom of the N−H bond with bulky groups (−R) leads to an increase in the interaction energy of the YR-HX complexes. Hence, it was found that the replacement of N-atom in N-heterocyclic carbene (NHC) by S-atom forming N-aryl-thiazol-2-ylidene results in comparable intermolecular interactions with proton donor molecules similar to imidazole-2-ylidene (NHC). The current study enlightened the role of noncovalent interactions in carbene complexes with proton donor molecules. We hope that our work on carbene chemistry will pave the way for its application in the designing and synthesis of efficient catalysts. 相似文献
789.
Swadhin Chetia Samprity Sarmah Dr. Apurba Dutta Prof. Diganta Sarma 《European journal of organic chemistry》2023,26(26):e202300390
A copper acetate monohydrate catalyzed simple, effective and economic protocol has been developed for the construction of quinazoline derivatives via acceptorless dehydrogenative coupling of easily available 2-aminoaryl methanols and nitriles. The methodology was also highly effective for the synthesis of medicinally important quinolines analogues. The reactions proceeded in presence of KOtBu in toluene at 110 °C for 5 h without the requirement of inert condition, external additives and ligands. 相似文献
790.
Shaik Sultana Dr. Godugu Kumar Dr. Loka Subramanyam Sarma Prof. Dr. Vemula Venkatramu Prof. Dr. Nallagondu Chinna Gangi Reddy 《European journal of organic chemistry》2023,26(10):e202300032
For the first time, interstitial nitrogen-doped TiO2 nanotubes (INDTNTs) have been utilized as heterogeneous green catalysts for the synthesis of D-π-A-type Knoevenagel adducts ( 3 ) and β-enaminones ( 6 ). Notable advantages of the present method include its wide substrate scope, low catalyst loading, avoiding the use of hazardous bases and solvents, products do not require chromatographic purification, high yields, catalyst reusability, etc. The optimized catalyst, INDTNTs-4 has been characterized by XRD, HRTEM, and XPS techniques. The photophysical and electrochemical properties of D-π-A-type 3 and 6 have been evaluated. The study revealed that the colour tunability (cold white light to orange light) and the HOMO/LUMO levels depend mainly on the presence of various electron donating and withdrawing groups on the aromatic/heteroaromatic rings of 3 and 6 . The results indicate that the D-π-A-type 3 and 6 could be promising materials for the fabrication of optoelectronic devices. 相似文献