Multiple Quanta Research Articles

Memory-Efficient Recursive Evaluation of 3-Center Gaussian Integrals.

To improve the efficiency of Gaussian integral evaluation on modern accelerated architectures, FLOP-efficient Obara-Saika-based recursive evaluation schemes are optimized for the memory footprint. For the 3-center 2-particle integrals that are key for the evaluation of Coulomb and other 2-particle interactions in the density-fitting approximation, the use of multiquantal recurrences (in which multiple quanta are created or transferred at once) is shown to produce significant memory savings. Other innovations include leveraging register memory for reduced memory footprint and direct compile-time generation of optimized kernels (instead of custom code generation) with compile-time features of modern C++/CUDA. Performance of conventional and CUDA-based implementations of the proposed schemes is illustrated for both the individual batches of integrals involving up to Gaussians with low and high angular momenta (up to L = 6) and contraction degrees, as well as for the density-fitting-based evaluation of the Coulomb potential. The computer implementation is available in the open-source LibintX library.

Observation of multiple fractional quanta in a superconducting bilayer disk with a pinhole

The magnetic-flux quantum (Φ0) cannot be generally divided into smaller ones in a usual superconductor. If a subdividing path is present, the science and technology of the superconductor drastically change. In previous studies, we experimentally presented a new, easy way to subdivide Φ0 into smaller quanta (Φf) using an ultrathin Nb bilayer with a through-pinhole (H. Ishizu, H. Yamamori, S. Arisawa, K. Tokiwa, Y. Tanaka, Physica C 595 (2022) 1354029.). However, because of an experimental technical problem, we could not use a higher field to generate more than one Φf. It was not clear if multiples of Φf could be trapped in a pinhole (in a usual superconductor, multiples of Φ0 are trapped in a pinhole). In this study, we observed multiple fractional phase shifts with a direct-current superconducting interference device (SQUID) placed on an ultrathin Nb bilayer disk containing a through-pinhole using an improved modification of an experimental procedure. The phase shift for the SQUID with the bilayer disk is an integer multiple of a basic fractional phase shift divided by 2π. However, we did not observe the fractional phase shift for a SQUID with a single-layer disk. These observations indicate that multiple fractional flux quanta are trapped in the bilayer disk. According to the vortex-molecule model, if the vortex molecule is larger than the bilayer disk, such quanta can be trapped. This is one example of altering a fundamental (universal) physical constant. The SQUID can more sensitively detect Φf than Φ0, rendering the design of novel superconducting electronics possible.

High-resolution infrared spectroscopy of supersonically cooled singlet carbenes: Bromomethylene (HCBr) in the CH stretch region.

First high-resolution spectra of cold (∼35K) singlet bromomethylene HCBr in the CH stretching (v1) region from 2770 to 2850cm-1 are reported using near quantum shot-noise limited laser absorption methods in a slit jet supersonic discharge expansion source. Three rovibrational bands are identified at high S/N (20:1-40:1) and rotationally assigned to (i) the CH stretch fundamental (v1) band X̃1,0,0←X̃0,0,0 and (ii) vibrational hot bands [X̃(1,1,0)←X̃(0,1,0) and X̃(1,0,1)←X̃(0,0,1)] arising from vibrationally excited HCBr populated in the discharge with single quanta in either the H-C-Br bend (v2) or C-Br stretch (v3) modes. Precision rotational constants are reported for a total of six states, with an experimentally determined CH stretch vibrational frequency (2799.38cm-1) in good agreement with previous low-resolution fluorescence studies [M. Deselnicu et al., J. Chem. Phys. 124(13), 134302 (2006)]. Detailed analysis of the fundamental v1 band highlights the presence of perturbations in the X̃1,0,0 level, which we tentatively attribute to arise from the nearby triplet state ã(0,0,1) through spin-orbit interaction or the multiple quanta X̃0,2,1 singlet state via c-type Coriolis coupling. Reduced-Doppler resolution (60MHz) in the slit-jet IR spectrometer permits for clear observation of a nuclear spin hyperfine structure, with experimental line shapes well reproduced by nuclear quadrupole/spin-rotation coupling constants from microwave studies [C. Duan et al., J. Mol. Spectrosc. 220(1), 113-121 (2003)]. Finally, the a-type to b-type transition intensity ratio for the fundamental CH stretch band is notably larger than that predicted by using a bond-dipole model, which from high level ab initio quantum calculations [CCSD(T)/PVQZ] can be attributed to vibrationally induced "charge-sloshing" of electron density along the polar C-Br bond.

Low lying oscillations of deformed nuclei

Low-lying oscillations of the intrinsic deformed shape of a nucleus remain an open challenge in nuclear structure. The question or challenge revolves around the viability of single or multiple quanta of vibrational excitations superimposed on the equilibrium, deformed shape of a nucleus. The K=2 or “γ” vibrations are fairly widespread and nominally conform to expectations whereas the existence of the K=0 or “β” vibrational excitation is yet to be distinguished from other possible origins including the coexistence of other potential minima.

Single-Site Tetracoordinated Aluminum Hydride Supported on Mesoporous Silica. From Dream to Reality!

The reaction of mesoporous silica (SBA15) dehydroxylated at 700 °C with diisobutylaluminum hydride, i-Bu2AlH, gives after thermal treatment a single-site tetrahedral aluminum hydride with high selectivity. The starting aluminum isobutyl and the final aluminum hydride have been fully characterized by FT-IR, advanced SS NMR spectroscopy (1H, 13C, multiple quanta (MQ) 2D 1H–1H, and 27Al), and elemental analysis, while DFT calculations provide a rationalization of the occurring reactivity. Trimeric i-Bu2AlH reacts selectively with surface silanols without affecting the siloxane bridges. Its analogous hydride catalyzes ethylene polymerization. Indeed, catalytic tests show that this single aluminum hydride site is active in the production of a high-density polyethylene (HDPE).

Quantum packet for the next generation network/ISDN3

This paper proposes a novel method for transporting various types of user traffic effectively over the next generation network called integrated services digital network 3 (ISDN3) (or quantum network) using quantum packets. Basically, a quantum packet comprises one or more 53-byte quanta as generated by a “quantumization” process. While connection-oriented traffic is supported by fixed-size quantum packets each with one quantum to emulate circuit switching, connectionless traffic (e.g., IP packets and active packets) is carried by variable-size quantum packets with multiple quanta to support store-and-forward switching/routing. Our aim is to provide frame-like or datagram-like services while enabling cell-based multiplexing. The quantum packet method also establishes a flexible and extensible framework that caters for future packetization needs while maintaining backward compatibility with ATM. In this paper, we discuss the design of the quantum packet method, including its format, the “quantumization” process, and support for different types of user traffic. We also present an analytical model to evaluate the consumption of network resources (or network costs) when quantum packets are employed to transfer loss-sensitive data using three different approaches: cut-through, store-and-forward and ideal. Close form mathematical expressions are obtained for some situations. In particular, in terms of network cost, we discover two interesting equivalence phenomena for the cut-through and store-and-forward approaches under certain conditions and assumptions. Furthermore, analytical and simulation results are presented to study the system behavior. Our analysis provides valuable insights into the design of the ISDN3/quantum network.

Action Potential-Independent and Nicotinic Receptor-Mediated Concerted Release of Multiple Quanta at Hippocampal CA3–Mossy Fiber Synapses

Presynaptic action potential-independent transmitter release is a potential means of information transfer across synapses. We show that in the hippocampal mossy fiber boutons, activation of the alpha7-subtype of nicotinic acetylcholine receptors (alpha7-nAChRs) results in a large increase in the amplitude of spontaneous events, resulting from concerted release of multiple quanta from the mossy fiber boutons. This amplitude increase is abolished at low temperatures. Activation of alpha7-nAChRs causes a rise in intraterminal calcium at mossy fiber boutons, involving ryanodine receptors. Regulation of concerted release requires the subsequent activation of presynaptic calcium/calmodulin-dependent protein kinase II (CaMKII). Activation of CaMKII is required to drive presynaptic action potential-independent transmission at the mossy fiber-CA3 pyramidal cell synapse. The effects of alpha7-nAChR activation are mediated by biologically relevant doses of nicotine. Our results demonstrate a novel form of synaptic plasticity mediated by presynaptic alpha7-nAChRs and store calcium that is temporally different and might respond to a different history of synaptic activity than that mediated by incoming action potentials.

Structural and spatially resolved studies on the hardening of a commercial resin-modified glass-ionomer cement

A commercial photopolymerizable resin-modified glass-ionomer (Fuji II LC) was studied using a variety of nuclear magnetic resonance (NMR) techniques. (1)H and (19)F stray-field imaging (STRAFI) enabled to follow the acid-base reaction kinetics in self-cured (SC) samples. Gelation and maturation processes with 25 min and 40 h average time constants, respectively, were distinguished. In self- & photo-cured (SPC) samples, two processes were also observed, which occurred with 2 s and 47 s average time constants. (1)H, (27)Al and (29)Si magic angle spinning (MAS) NMR, (13)C cross-polarization (CP)/MAS NMR and (27)Al multiple quanta (MQ)MAS NMR spectroscopy were used to obtain structural information on the glass and cements that were either SC or SPC. The presence of methacrylate groups was identified in the solid component. Unreacted hydroxyl ethylmethacrylate (HEMA) was detected in self-cured cement. (27)Al data showed that approximately 28% and 20% of Al is leached out from glass particles in SC and SPC samples, respectively. The upfield shift detected in (29)Si MAS NMR spectra of the cements is consistent with a decrease in the number of Al species in the second coordination sphere of the silicon structures. Scanning electron microscopy (SEM) showed existence of 3D shrinkage of the cement matrix in photo-cured cements.

Maximizing Your Minis

Sharma and Vijayaraghavan investigated the modulation of neurotransmitter release from quiescent hippocampal neurons and discovered that calcium entering through presynaptic nicotinic acetylcholine receptors (nAChRs) led to bursts of glutamate release that were sufficient to drive the postsynaptic cell to threshold. Resting neurons spontaneously release the contents of individual synaptic vesicles at random intervals. The ensuing miniature postsynaptic potentials, which correspond to individual quanta of the postsynaptic response, are too small to affect firing in the postsynaptic cell, and their physiological function has remained obscure (see Preview by Zucker). Sharma and Vijayaraghavan recorded miniature excitatory postsynaptic currents (mEPSCs) from voltage-clamped CA3 pyramidal cells in rat hippocampal slices before, during, and after local application of nicotine. Nicotine increased the fraction of large mEPSCs in a manner consistent with the concerted release of multiple quanta and stimulated the production of high-frequency bursts of mEPSCs. Pharmacological analysis in combination with manipulation of the extracellular calcium concentration indicated that this increase in mEPSC amplitude and frequency depended on release of calcium from intracellular stores secondary to calcium influx through presynaptic nAChRs. When voltage clamp was released, glutamate released in response to nicotine application initiated bursts of action potentials in the postsynaptic cells. Thus, calcium influx through presynaptic nAChRs appears to provide a mechanism whereby impulses can be generated in the postsynaptic cell independent of the firing of the presynaptic neuron. G. Sharma, S. Vijayaraghavan, Modulation of presynaptic store calcium induces release of glutamate and postsynaptic firing. Neuron 38 , 929-939 (2003). [Online Journal] R. S. Zucker, Can a synaptic signal arise from noise? Neuron 38 , 845-846 (2003). [Online Journal]

Feedback-current-injection-type second-order lowpass sigma-delta modulator

In order to establish double-loop feedback design, we have fabricated a prototype superconducting double-loop lowpass sigma-delta modulator. For digital feedback gain, multiple flux quanta are produced by a ladder circuit and carried through Josephson Transmission Lines (JTLs) to the feedback driver. The feedback driver consists of a single Josephson junction or two serially-connected junctions. Direct injection of the pulse current from the JTLs through a low-value resistor drives the feedback driver. The sigma-delta modulator was operated at the sampling frequency of 1.1 GHz and the measured power spectrum showed the noise shaping roughly of 12 dB/octave, which is characteristic of the second-order sigma-delta modulator.

Glutamate Uptake Limits Synaptic Excitation of Retinal Ganglion Cells

EPSCs of retinal ganglion cells decay more slowly than do those of most other CNS neurons, in part because of the long time course of glutamate release from bipolar cells. Here we investigated how glutamate clearance and AMPA receptor desensitization affect ganglion cell EPSCs in the salamander retinal slice preparation. Inhibition of glutamate uptake greatly prolonged ganglion cell EPSCs evoked by light or monosynaptic electrical stimuli but had little effect on spontaneous miniature EPSCs (mEPSCs). This suggests that single quanta of glutamate are cleared rapidly by diffusion but multiple quanta can interact to lengthen the postsynaptic response. Some interaction between quanta is likely to occur even when glutamate uptake is not inhibited. This seems to depend on quantal content, because reducing glutamate release with low Ca2+, paired-pulse depression, or weak stimuli shortened the EPSC decay. High quantal content glutamate release may lead to desensitization of postsynaptic receptors. We reduced the extent of AMPA receptor desensitization by holding ganglion cells at positive potentials. This increased the amplitude of the late phase of evoked EPSCs but did not affect the decay rate after the first 50 msec of the response. In contrast, the holding potential had little effect on mEPSC kinetics. Our results suggest that desensitization limits the late phase of AMPA receptor-mediated EPSCs, whereas glutamate uptake controls the duration of both AMPA and NMDA receptor-mediated responses.

A high-resolution HCANH experiment with enhanced sensitivity via multiple quantum line narrowing.

We report a 3D constant-time HCANH experiment (CTSL-HCANH) that uses the slower relaxation of multiple-quantum coherence to increase sensitivity and provides high C(α) resolution. In this experiment the H(α) of the (H(α), C(α)) multiple quanta are selectively spin locked, so that H(α) chemical shift evolution and (1) H-(1)H J-dephasing become ineffective during the relatively long delay needed for C(α) to N coherence transfer. As compared to an HCANH experiment that uses C(α) single-quantum coherence, an average enhancement of 20% was observed on calmodulin in complex with the binding domain of the transcription factor SEF2-1. Compared to CBCANH the signal intensity is approximately twice as good. The favorable relaxation properties of multiple quanta, together with the outstanding C(α) resolution, make the experiment a very good complement to CBCANH and CBCA(CO)NH for sequential assignment of larger proteins for which deuteration is not yet necessary.

A new sequence for the MQMAS/HETCOR experiment

Two-dimensional (2D) multiple quantum MAS (magic angle spinning) spectroscopy has been combined with cross-polarisation to obtain a heteronuclear correlation spectrum between a quadrupolar spin-3/2 and a spin-1/2 nucleus. The advantage over the conventional correlation experiment is the increased resolution obtained in the multiple quantum dimension. Pure absorption 2D spectra can be obtained by implementing a zero quantum filter between the evolution of multiple quanta and the subsequent cross-polarisation step. The current experiment shows a considerable improvement in sensitivity compared to a previously introduced sequence.

Vibrational energy transfer from four levels below 410 cm−1 in S1 p-difluorobenzene. I. A strong collision partner dependence in state-to-state transfer by monatomics

Collision-induced vibrational energy transfer has been studied from four levels [302 (Evib=240 cm−1), 82 (Evib=361 cm−1), 271 (Evib=403 cm−1) and 61 (Evib=410 cm−1)] in S1 p-difluorobenzene in supersonic free jet expansions of He, Ne, Ar, and Kr at ∼30–40 K. In broad terms the trends are similar to those observed previously in studies of aromatics: the transfer is highly selective, and one quantum changes in the low frequency modes are preferred. However, a significant collision partner dependence is observed, whereby changing from He through to Kr causes a substantial increase in multiple quanta (‖Δυ‖≳1) transfer. SSH-T calculations fail to capture this trend. The preference for ‖Δυ‖≳1 transfer appears to be enhanced as the interaction time and attractive force on the collision partner increase. Consequently, it is predicted that (i) differences in the state-to-state branching ratios between collision partners will increase as the temperature is lowered; (ii) for a particular collision partner there will be an increase in ‖Δυ‖≳1 transfer with decreasing temperature; and (iii) ‖Δυ‖≳1 transfers will be most important for collision partners with small velocities (i.e., large masses), large intermolecular potential well depths (ε) and size (σ). The nearly isoenergetic 271 and 61 levels have virtually identical state-to-state branching ratios for Ar and small differences are observed for He. This suggests that the branching ratios are not particularly sensitive to the initial vibrational motion. Relaxation of 61 and 271 is inefficient compared with relaxation from 302 and 82.

Multiple Quantum Transitions Induced by Irradiating Single Quantum Coherence in a Heteronuclear Spin System

AbstractIn a heteronuclear spin system, with initially prepared single quantum (SQ) coherence of X‐spin, the irradiation of the proton spins will induce all the possible transitions including those SQs and multiple quanta (MQs) available in the system to be studied. The MQs appear in a rather weak irradiation while a strong irradiation results in a complete decoupling situation. Theoretical analysis is made to explain this phenomenon and is agreed qualitatively with experiments in the CH2 group. This phenomenon of MQ induction may happen in a decoupling experiment, when the effective irradiation strength is rather weak and it may also provide a convenient approach to create and then to manipulate MQ coherences in heteronuclear spin systems.

The Fröhlich kinetic equation with additional terms

The Frohlich kinetic equation (FKE) describes the coherent excitation in a band of polarization waves consisting of normal modes. The FKE involves the one and two quanta terms representing energy supply, energy losses and energy channeling between the modes with the help of the heat bath. The energy channeling between the vibration systems located at different positions and the channeling connected with multiple quanta processes without the help of the heat bath are analyzed. The additional terms of the FKE are derived. The multiple quanta processes may channel the energy from the coherently excited mode (or modes) to higher frequency ones.