Dynamics of clusters: From elementary to biological structures

Between isolated atoms or molecules and bulk materials there lies a class of unique structures, known as clusters, that consist of a few to hundreds of atoms or molecules. Within this range of "nanophase," many physical and chemical properties of the materials evolve as a function of cluster size, and materials may exhibit novel properties due to quantum confinement effects. Understanding these phenomena is in its own rights fundamental, but clusters have the additional advantage of being controllable model systems for unraveling the complexity of condensed-phase and biological structures, not to mention their vanguard role in defining nanoscience and nanotechnology. Over the last two decades, much progress has been made, and this short overview highlights our own involvement in developing cluster dynamics, from the first experiments on elementary systems to model systems in the condensed phase, and on to biological structures

Evolution of entanglement spectra under generic quantum dynamics

We characterize the early stages of the approach to equilibrium in isolated quantum systems through the evolution of the entanglement spectrum. We find that the entanglement spectrum of a subsystem evolves with at least three distinct timescales. First, on an o(1) timescale, independent of system or subsystem size and the details of the dynamics, the entanglement spectrum develops nearest-neighbor level repulsion. The second timescale sets in when the light-cone has traversed the subsystem. Between these two times, the density of states of the reduced density matrix takes a universal, scale-free 1/f form; thus, random-matrix theory captures the local statistics of the entanglement spectrum but not its global structure. The third time scale is that on which the entanglement saturates; this occurs well after the light-cone traverses the subsystem. Between the second and third times, the entanglement spectrum compresses to its thermal Marchenko-Pastur form. These features hold for chaotic Hamiltonian and Floquet dynamics as well as a range of quantum circuit models.Comment: 12 pages, 15 figure

Non-Markovian finite-temperature two-time correlation functions of system operators: beyond the quantum regression theorem

An extremely useful evolution equation that allows systematically calculating the two-time correlation functions (CF's) of system operators for non-Markovian open (dissipative) quantum systems is derived. The derivation is based on perturbative quantum master equation approach, so non-Markovian open quantum system models that are not exactly solvable can use our derived evolution equation to easily obtain their two-time CF's of system operators, valid to second order in the system-environment interaction. Since the form and nature of the Hamiltonian are not specified in our derived evolution equation, our evolution equation is applicable for bosonic and/or fermionic environments and can be applied to a wide range of system-environment models with any factorized (separable) system-environment initial states (pure or mixed). When applied to a general model of a system coupled to a finite-temperature bosonic environment with a system coupling operator L in the system-environment interaction Hamiltonian, the resultant evolution equation is valid for both L = L^+ and L \neq L^+ cases, in contrast to those evolution equations valid only for L = L^+ case in the literature. The derived equation that generalizes the quantum regression theorem (QRT) to the non-Markovian case will have broad applications in many different branches of physics. We then give conditions on which the QRT holds in the weak system-environment coupling case, and apply the derived evolution equation to a problem of a two-level system (atom) coupled to a finite-temperature bosonic environment (electromagnetic fields) with L \neq L^+.Comment: To appear in the Journal of Chemical Physics (12 pages, 1 figure

Dynamical Coulomb Blockade Observed in Nano-Sized Electrical Contacts

Electrical contacts between nano-engineered systems are expected to constitute the basic building blocks of future nano-scale electronics. However, the accurate characterization and understanding of electrical contacts at the nano-scale is an experimentally challenging task. Here we employ low-temperature scanning tunneling spectroscopy to investigate the conductance of individual nano-contacts formed between flat Pb islands and their supporting substrates. We observe a suppression of the differential tunnel conductance at small bias voltages due to dynamical Coulomb blockade effects. The differential conductance spectra allow us to determine the capacitances and resistances of the electrical contacts which depend systematically on the island--substrate contact area. Calculations based on the theory of environmentally assisted tunneling agree well with the measurements.Comment: 5 pages, 3 figures, to appear in PR

Bare-handed 3D drawing in augmented reality

Head-mounted augmented reality (AR) enables embodied in situ drawing in three dimensions (3D).We explore 3D drawing interactions based on uninstrumented, unencumbered (bare) hands that preserve the user’s ability to freely navigate and interact with the physical environment. We derive three alternative interaction techniques supporting bare-handed drawing in AR from the literature and by analysing several envisaged use cases. The three interaction techniques are evaluated in a controlled user study examining three distinct drawing tasks: planar drawing, path description, and 3D object reconstruction. The results indicate that continuous freehand drawing supports faster line creation than the control point-based alternatives, although with reduced accuracy. User preferences for the different techniques are mixed and vary considerably between the different tasks, highlighting the value of diverse and flexible interactions. The combined effectiveness of these three drawing techniques is illustrated in an example application of 3D AR drawing

Synthesis, Anti-inflammatory and Anti-nociceptive Evaluation of Palmitoyl Benzamides

Purpose: To synthesize and characterize palmitoyl amino benzamides, and to evaluate them for possible anti-inflammatory and anti-nociceptive activities.Methods: Palmitoyl amino benzamides were synthesized by the opening of isatoic anhydride ring with respective amino acids (glycine, β-alanine and γ-aminobutyric acid) and the condensation of the product with palmitoyl chloride. The final products were purified on column chromatography, eluting with dichloromethane/ethyl acetate. All the compounds were unequivocally characterized using the combination of infra red (IR), 1H and 13C (nuclear magnetic resonance (NMR), mass spectrometry (MS) and elemental analysis. In vivo anti-inflammatory and anti-nociceptive activities of the synthesized compounds at 20, 50 and 100mg/kg doses were carried out using carrageenan-induced paw oedema in rat and acetic acid-induced writhing in mice, respectively. Aspirin was used at a dose of 100mg/kg as the reference drug.Results: The compounds were obtained in high yield (70 – 90 %) and purity. The anti-inflammatory results showed a poor activity for the compounds except o-palmitoylamino N-carboxyethyl benzamide which produced significant inhibition (p < 0.05) at a dose of 50 mg/kg (43.8 % oedema inhibition) while the reference drug, aspirin, showed 51.3 % inhibition. The anti-nociceptive study, however, showed good inhibition (p < 0.05) of acetic acid-induced writhing, with o-palmitoylamino Ncarboxymethylbenzamide producing 86.2 % inhibition at 100 mg/kg dose compared with the reference drug (aspirin) which gave 74.3 % inhibition at 100 mg/kg.Conclusion: The findings of this study indicate that the synthesized compounds, though displaying poor anti-inflammatory activity, do possess promising anti-nociceptive activity.Keywords: Anti-inflammatory, Analgesic, Benzamide, Palmitoyl, Glycine, β-Alanine, γ-Aminobutyric acid, Aspiri