National Institute of Physics

This study aimed to evaluate the use of a dielectric barrier discharge (DBD) plasma system to improve the safety of pork loins. When pork loin was exposed to DBD plasma with the input gases He and He þ O 2 , the population of Escherichia coli was reduced by 0.26 and 0.50 log cycles following a 5-min treatment and by 0.34 and 0.55 log units following a 10-min treatment, respectively. That of Listeria monocytogenes was also reduced from 0.17 to 0.35 and 0.43 to 0.59 log cycles when the samples were exposed to DBD for 5 and 10 min using He and He þ O 2 , respectively. The pH and L*-values (lightness) of the samples decreased significantly with DBD plasma treatment, but a*-(redness) and b*-values (yellowness) exhibited no obvious changes. Lipid oxidation, measured by TBARS values, was greater in samples with He þ O 2 than in other samples. Significant reductions in sensory quality parameters (appearance, color, odor, acceptability, etc.) were observed in DBD-treated samples. These results indicate that the DBD plasma system has potential for use in sanitizing pork loins by inactivation of foodborne pathogens, although the effect was limited. In order to meet market requirements, however, a method to overcome sensory deterioration of pork loins should be developed and applied.

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We present a continuous time generalization of a random walk with complete memory of its history [Phys. Rev. E 70, 045101(R) (2004)] and derive exact expressions for the first four moments of the distribution of displacement when the number of steps is Poisson distributed. We analyze the asymptotic behavior of the normalized third and fourth cumulants and identify new transitions in a parameter regime where the random walk exhibits superdiffusion. These transitions, which are also present in the discrete time case, arise from the memory of the process and are not reproduced by Fokker-Planck approximations to the evolution equation of this random walk.

We give an exact solution to the generalized Langevin equation of motion of a charged Brownian particle in a uniform magnetic field that is driven internally by an exponentially correlated stochastic force. A strong dissipation regime is described in which the ensemble-averaged fluctuations of the velocity exhibit transient oscillations that arise from memory effects. Also, we calculate generalized diffusion coefficients describing the transport of these particles and briefly discuss how they are affected by the magnetic field strength and correlation time. Our asymptotic results are extended to the general case of internal driving by correlated Gaussian stochastic forces with finite autocorrelation times.

We study the statistics of the work done in a zero temperature quench of the coupling constant in the Dicke model describing the interaction between an ensemble of two level systems and a single bosonic mode. When either the final or the initial coupling constants approach the critical coupling λc that separates the normal and superradiant phases of the system, the probability distribution of the work done displays singular behavior. The average work tends to diverge as the initial coupling parameter is brought closer to the critical value λc. In contrast, for quenches ending close to criticality, the distribution of work has finite moments but displays a sequence of edge singularities. This contrasting behavior is related to the difference between the processes of compression and expansion of a particle subject to a sudden change in its confining potential. We confirm this by studying in detail the time-dependent statistics of other observables, such as the quadratures of the photons and the total occupation of the bosonic modes.

We calculate the first order perturbation correction to the ground state energy and chemical potential of a harmonically trapped boson gas with contact interactions about the infinite repulsion Tonks-Girardeau limit. With c denoting the interaction strength, we find that for a large number of particles N the 1/c correction to the ground state energy increases as N^5/2, in contrast to the unperturbed Tonks-Girardeau value that is proportional to N^2. We describe a thermodynamic scaling limit for the trapping frequency that yields an extensive ground state energy and reproduces the zero temperature thermodynamics obtained by a local density approximation.

We quantify the extractable entanglement of excited states of a Lieb-Liniger gas that are obtained from coarse-grained measurements on the ground state in which the boson number in one of two complementary contiguous partitions of the gas is determined. Numerically exact results obtained from the coordinate Bethe ansatz show that the von Neumann entropy of the resulting bipartite pure state increases monotonically with the strength of repulsive interactions and saturates to the impenetrable boson limiting value. We also present evidence indicating that the largest amount of entanglement can be extracted from the most probable projected state having half the number of bosons in a given partition. Our study points to a fundamental difference between the nature of the entanglement in free-bosonic and free-fermionic systems, with the entanglement in the former being zero after projection, while that in the latter (corresponding to the impenetrable boson limit) being non-zero.

We exactly calculate the reduced density matrix of matrix product states (MPS). Our compact result enables one to perform analytic studies of entanglement in MPS. In particular, we consider the MPS ground states of two anisotropic spin chains. One is a q-deformed Affleck-Kennedy-Lieb-Tasaki (AKLT) model and the other is a general spin-1 quantum antiferromagnet with nearest-neighbor interactions. Our analysis shows how anisotropy affects entanglement on different continuous parameter manifolds. We also construct an effective boundary spin model that describes a block of spins in the ground state of the q-deformed AKLT Hamiltonian. The temperature of this effective model is given in terms of the deformation parameter q.

We calculate the reduced density matrix of a block of integer spin-S's in a q-deformed valence-bond-solid (VBS) state. This matrix is diagonalized exactly for an infinitely long block in an infinitely long chain. We construct an effective Hamiltonian with the same spectrum as the logarithm of the density matrix. We also derive analytic expressions for the von Neumann and Rényi entanglement entropies. For blocks of finite length, we calculate the eigenvalues of the reduced density matrix by perturbation theory and numerical diagonalization. These results enable us to describe the effects of finite-size corrections on the entanglement spectrum and entropy in this generalized VBS model.

We study a one-dimensional multicomponent anyon model that reduces to a multicomponent Lieb-Liniger gas of impenetrable bosons (Tonks-Girardeau gas) for vanishing statistics parameter. At fixed component densities, the coordinate Bethe ansatz gives a family of quantum phase transitions at special values of the statistics parameter. We show that the ground-state energy changes extensively between different phases. Special regimes are studied and a general classification for the transition points is given. An interpretation in terms of statistics of composite particles is proposed.

We study entanglement between the spin components of the Bardeen-Cooper-Schrieffer (BCS) ground state by calculating the full entanglement spectrum and the corresponding von Neumann entanglement entropy. The entanglement spectrum is effectively modeled by a generalized Gibbs ensemble (GGE) of non-interacting electrons, which may be approximated by a canonical ensemble at the BCS critical temperature. We further demonstrate that the entanglement entropy is jointly proportional to the pairing energy and to the number of electrons about the Fermi surface (an area law). Furthermore, the entanglement entropy is also proportional to the number fluctuations of either spin component in the BCS state.

We derive exact analytic expressions for the average work done and work fluctuations in instantaneous quenches of the ground and thermal states of a one-dimensional anisotropic XY model. The average work and a quantum fluctuation relation is used to determine the amount of irreversible entropy produced during the quench, eventually revealing how the closing of the excitation gap leads to increased dissipated work. The work fluctuation is calculated and shown to exhibit non-analytic
behavior as the pre-quench anisotropy parameter and transverse field are tuned across quantum critical points. Exact compact formulas for the average work and work fluctuation in ground state quenches of the transverse field Ising model allow us to calculate the first singular field derivative at the critical field values.

We report tip-enhanced broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy and imaging based on a broadband light source using a photonic crystal fiber. Multiplexing from 900 cm -1 to 2200 cm -1 is achieved by optimizing the supercontinuum generation process at a high numerical aperture focus. By combining this system with a shear-force microscope, semiconducting carbon nanotubes are imaged with a spatial resolution of 60 nm. Our results show that tip-enhanced broadband CARS image exhibits a positive contrast even though the enhancement effect has not been fully optimized. Analyses of delaydependent tip-enhanced broadband CARS spectra suggest the possibilities of multiple carrier interactions that uniquely occur at high intensities within the nanotubes.

Liquid crystals (LC) are partly structured fluids composed of molecules that are usually elongated in shape. Under appropriate conditions, these molecules exhibit a certain degree of orientational order, such that the molecules spontaneously align towards a certain axis described by the director n (x,y,z) [1]. The spatial configuration of the director is highly sensitive to several factors such as temperature, electric or magnetic fields, and molecular interactions at the bounding surface . Accurate visualization of n, therefore, is critical to understanding the properties of these materials and to further improve the technologies utilizing them. Here, we report fast spectroscopic imaging of a nematic liquid crystal using a supercontinuum generated from a photonic crystal fiber as the Stokes pulse. The broadband Stokes beam allows for simultaneous detection of the CARS signal over a wide frequency region. Moreover, we demonstrate that by combining the system with the principles of polarization microscopy, broadband CARS can provide a detailed characterization of the three-dimensional orientation of a specific molecular bond.

We report parallel two-photon photopolymerization of microgear patterns by exposing a photoresist to holographically generated optical vortices. The optical vortices are created by imparting a helical pitch onto the incident light using a programmable lithographic phase mask realized with a computer addressable phase-only spatial light modulator. By varying the phase levels of the spatial light modulator, the truncated helical phase of an optical vortex results in output intensity patterns that typifies that of microgears instead of perfect doughnut beams. Our experiments and simulations are in good agreement implying a more efficient and highly parallel two-photon photopolymerization scheme that can be subsequently used for non-scanning fabrication of microgears.

A technique is demonstrated for extending the dynamic range of 1-bit analog-to-digital converters (ADCs) that sample at the maximum rate using a sinusoid reference ( ) = cos(2 ). The ADC has a detection limit = 1, where 2 is the base-clock period, and 1 = sampling interval = 1 2 2 . Optimal sampling is achieved at 1 = 2 , but with large quantization errors found in the sampled representation of the input signal ( ). Dithering with noise ( ) of appropriate variance 2 is utilized to measure a subthreshold ( ) where ( ) for all . Both uniform white noise (UWN) and Gaussian white noise (GWN) are utilized. With UWN dithering at = , we could reduce the errors to levels that are produced by an equivalent -bit amplitude-sampling (bipolar) ADC by observing the dithered signal ( ) + ( ) over a time duration of [(0 116 )(2 1)] 0 995 , where is the sampling period, and are the ADC supply voltages. With GWN dithering at = 0 5 , the duration required is [(0 109 )(2 1)] 0 996 . Index Terms-1-bit analog-to-digital conversion (ADC), crossing sampling, noise dithering.