Ultrasmall Nanodiamonds: Perspectives and Questions

Nanodiamonds are at the heart of a plethora of emerging applications in areas ranging from nanocomposites and tribology to nanomedicine and quantum sensing. The development of alternative synthesis methods, a better understanding, and the availability of ultrasmall nanodiamonds of less than 3 nm size with a precisely engineered composition, including the particle surface and atomic defects in the diamond crystal lattice, would mark a leap forward for many existing and future applications. Yet today, we are unable to accurately control nanodiamond composition at the atomic scale, nor can we reliably create and isolate particles in this size range. In this perspective, we discuss recent advances, challenges, and opportunities in the synthesis, characterization, and application of ultrasmall nanodiamonds. We particularly focus on the advantages of bottom-up synthesis of these particles and critically assess the physicochemical properties of ultrasmall nanodiamonds, which significantly differ from those of larger particles and bulk diamond

Ordering effect of Coulomb interaction in ballistic double-ring systems

We study a model of two concentric onedimensional rings with incommensurate areas $A_1$ and $A_2$, in a constant magnetic field. The two rings are coupled by a nonhomogeneous inter-ring tunneling amplitude, which makes the one-particle spectrum chaotic. For noninteracting particles the energy of the many-body ground state and the first excited state exhibit random fluctuations characterized by the Wigner-Dyson statistics. In contrast, we show that the electron-electron interaction orders the magnetic field dependence of these quantities, forcing them to become periodic functions, with period $\propto 1/(A_1 + A_2)$. In such a strongly correlated system the only possible source of disorder comes from charge fluctuations, which can be controlled by a tunable inter-ring gate voltage.Comment: 4 pages, 4 eps figures, revised text and new figures (as published

Controlled dephasing of Andreev states in superconducting quantum point-contacts

We have studied the relaxation and dephasing processes in a superconducting quantum point contact induced by the interaction with an electromagnetic environment. Based on a density matrix approach we obtain the rates for the dissipative dynamics as function of the transmission, the phase difference on the contact and the external impedance. Our calculation allows to determine the appropriate range of parameters for the observation of coherent oscillations in the current through the contact.Comment: 8 pages, 2 figures. To appear in Physical Review

Transport spectroscopy in a time-modulated open quantum dot

We have investigated the time-modulated coherent quantum transport phenomena in a ballistic open quantum dot. The conductance $G$ and the electron dwell time in the dots are calculated by a time-dependent mode-matching method. Under high-frequency modulation, the traversing electrons are found to exhibit three types of resonant scatterings. They are intersideband scatterings: into quasibound states in the dots, into true bound states in the dots, and into quasibound states just beneath the subband threshold in the leads. Dip structures or fano structures in $G$ are their signatures. Our results show structures due to 2$\hbar\omega$ intersideband processes. At the above scattering resonances, we have estimated, according to our dwell time calculation, the number of round-trip scatterings that the traversing electrons undertake between the two dot openings.Comment: 8 pages, 5 figure

Relation Between Chiral Susceptibility and Solutions of Gap Equation in Nambu--Jona-Lasinio Model

We study the solutions of the gap equation, the thermodynamic potential and the chiral susceptibility in and beyond the chiral limit at finite chemical potential in the Nambu--Jona-Lasinio (NJL) model. We give an explicit relation between the chiral susceptibility and the thermodynamic potential in the NJL model. We find that the chiral susceptibility is a quantity being able to represent the furcation of the solutions of the gap equation and the concavo-convexity of the thermodynamic potential in NJL model. It indicates that the chiral susceptibility can identify the stable state and the possibility of the chiral phase transition in NJL model.Comment: 21 pages, 6 figures, misprints are correcte

Alternative splicing and genetic diversity of the white collar-1 (wc-1) gene in cereal Phaeosphaeria pathogens

The white collar-1 (wc-1) gene encodes an important light-responsive protein (wc-1) that maintains circadian clocks and controls numerous light-dependent reactions including sporulation in ascomycete fungi. The structure and expression of the wc-1 gene in wheat-biotype Phaeosphaeria nodorum (PN-w) was studied. It was shown that the full-size (3,353 bp in length) wc-1 gene in PN-w contained 4 introns in which introns 1 and 2 were flanked by GC-AG splice borders and were spliced constitutively. However, introns 3 and 4 of the wc-1 gene were alternatively spliced. As the result of alternative splicing (AS), six transcript variants were identified, encoding different lengths of deduced polypeptides (from 1,044 to 1,065aa). Ratios of the wc-1 gene transcript variants in the RNA population were the same in the sporulated and non-sporulated PN-w isolate Sn37-1 and the sporulated PN-w isolate S-79-1, grown under light/dark conditions. The AS of the wc-1 gene may control various light-dependent reactions in PN-w, which leads to diverse morphological, physiological and pathological characters for pathogen infection and spread. Based on the nucleotide and deduced amino acid sequences, the wc-1 gene in cereal Phaeosphaeria pathogens was diverse. It appeared that the deduced wc-1 polypeptide sequences of P. avenaria f. sp. avenaria (Paa), P. avenaria f. sp. triticea (Pat1 and Pat3) and barley biotype P. nodorum (PN-b) were more closely related than PN-w and Phaeosphaeeria sp. (P-rye) from Poland. Based on the wc-1 deduced polypeptide sequences, P. avenaria f. sp. triticea (Pat2) from foxtail barley (Hordeum jubatum L.) was evolutionary well separated from the other cereal Phaeosphaeria pathogens

Cloning of the gene and characterization of the enzymatic properties of the monomeric alkaline phosphatase (PhoX) from Pasteurella multocida strain X-73

We have identified a new phoX gene encoding the monomeric alkaline phosphatase from Pasteurella multocida X-73. This gene was not found in the published genome sequence of Pasteurella multocida pm70. Characterization of the recombinant PhoX of Pasteurella multocida X-73 showed that it is a monomeric enzyme, activated by Ca2+ and possibly secreted by the Tat pathway. These features distinguish phosphatases of the PhoX family from those of the PhoA family. All proteins of the PhoX family were found to contain a conserved motif that shares significant sequence homology with the calcium-binding site of a phosphotriesterase known as diisopropylfluorophosphatase. Site-directed mutagenesis revealed that D527 of PhoX might be the ligand bound to the catalytic calcium. This is the first report on identification of homologous sequences between PhoX and the phosphotriesterase and on the potential calcium-binding site of PhoX

Spectral Correlation in Incommensurate Multi-Walled Carbon Nanotubes

We investigate the energy spectra of clean incommensurate double-walled carbon nanotubes, and find that the overall spectral properties are described by the so-called critical statistics of Anderson metal-insulator transition. In the energy spectra, there exist three different regimes characterized by Wigner-Dyson, Poisson, and semi-Poisson distributions. This feature implies that the electron transport in incommensurate multi-walled nanotubes can be either diffusive, ballistic, or intermediate between them, depending on the position of the Fermi energy.Comment: final version to appear in Phys. Rev. Let

Observation of Two New N* Peaks in J/psi -> ppi−nˉp pi^- \bar n and pˉπ+n\bar p\pi^+n Decays

The $\pi N$ system in decays of $J/\psi\to\bar NN\pi$ is limited to be isospin 1/2 by isospin conservation. This provides a big advantage in studying $N^*\to \pi N$ compared with $\pi N$ and $\gamma N$ experiments which mix isospin 1/2 and 3/2 for the $\pi N$ system. Using 58 million $J/\psi$ decays collected with the Beijing Electron Positron Collider, more than 100 thousand $J/\psi \to p \pi^- \bar n + c.c.$ events are obtained. Besides two well known $N^*$ peaks at 1500 MeV and 1670 MeV, there are two new, clear $N^*$ peaks in the $p\pi$ invariant mass spectrum around 1360 MeV and 2030 MeV. They are the first direct observation of the $N^*(1440)$ peak and a long-sought "missing" $N^*$ peak above 2 GeV in the $\pi N$ invariant mass spectrum. A simple Breit-Wigner fit gives the mass and width for the $N^*(1440)$ peak as $1358\pm 6 \pm 16$ MeV and $179\pm 26\pm 50$ MeV, and for the new $N^*$ peak above 2 GeV as $2068\pm 3^{+15}_{-40}$ MeV and $165\pm 14\pm 40$ MeV, respectively