Soil Chemical Analysis

Quantum tunnelling in a dissipative system

It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.

a Quantum-Mechanical Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals.

Squeezed states of the electromagnetic field have been generated by nondegenerate four-wave mixing due to Na atoms in an optical cavity. The optical noise in the cavity, comprised of primarily vacuum fluctuations and a small component of spontaneous emission from the pumped Na atoms, is amplified in one quadrature of the optical field and deamplified in the other quadrature. These quadrature components are measured with a balanced homodyne detector. The total noise level in the deamplified quadrature drops below the vacuum noise level.

Observation of squeezed states generated by four-wave mixing in an optical cavity

The Jaynes-Cummings model (JCM), a soluble fully quantum mechanical model of an atom in a field, was first used (in 1963) to examine the classical aspects of spontaneous emission and to reveal the existence of Rabi oscillations in atomic excitation probabilities for fields with sharply defined energy (or photon number). For fields having a statistical distributions of photon numbers the oscillations collapse to an expected steady value. In 1980 it was discovered that with appropriate initial conditions (e.g. a near-classical field), the Rabi oscillations would eventually revive, only to collapse and revive repeatedly in a complicated pattern. The existence of these revivals, present in the analytic solutions of the JCM, provided direct evidence for discreteness of field excitation (photons) and hence for the truly quantum nature of radiation. Subsequent study revealed further non-classical properties of the JCM field, such as a tendency of the photons to antibunch. Within the last two years it ha...

The Jaynes-Cummings Model

Photon statistics in some fully quantized models of the interaction of a two-level atom with a single-mode radiation field have been studied using the operator equations of motion. Expressions for the photon number distribution and the mean photon number are presented for various initial conditions. It is found that the mean photon number may show decays and revivals of coherence similar to those of the atomic inversion in the coherent-state Jaynes-Cummings model. Application of these models to the study of multiphoton laser, absorption, and emission processes is also discussed.

Field statistics in some generalized Jaynes-Cummings models

Photoelectron counting sequences for single-atom resonance fluorescence are studied. The distribution of waiting times between photoelectric counts is calculated, and its dependence on drivingfield intensity and detection efficiency is discussed. The photoelectron-counting distribution is derived from the waiting-time distribution. The relationship between photoelectron counting sequences and photon emission sequences is discussed and used to obtain an expression for the reduced state of the atom during the waiting times between photoelectric counts. The roles of irreversibility and the observer in atomic state reduction are delineated. The fluorescent photons emitted by a single coherently driven two-level atom exhibit the nonclassical property of photon antib~nchin~.l-~ The antibunching of fluorescent photons is seen in temporal correlations between photoelectric counts; the detection of one photon makes the detection of a second, after just a short delay, improbable. Photon antibunching is traditionally defined in terms of the degree of second-order temporal coherence g'2'( t, t +T). This is the joint probability for recording photoelectric counts in the intervals [t,t +At) and [t +T, t +7+At), normalized by the probability for two independent photoelectric counts. For antibunched light the joint probability for recording photoelectric counts closely spaced in time falls below the probability for statistically independent counts (separated by a time longer than the coherence time); thus, gi2'( t, t) < 1. The antibunching of fluorescent photons is also reflected in the sub-Poissonian character of the probability density p (n, t, t + TI for recording n photoelectric counts in the interval [r, t + T).~ p (n,t,t + T) can be derived from g'2'(t,t +T), although the detailed algebraic relationship is quite complicated. Both g'2'(t,t +T) and p (n, t, t + T) have been calculated for single-atom resonance fluorescence by a number of workers.'-lo Because of the complexity of general expressions in the time domain, some workers only give the Laplace transform for the photoelectron counting distribution, or give explicit time-dependent expressions only for limiting cases, such as short and long counting times. Recent theoretical work on "quantum j~rn~s""~~~ has drawn attention to the distribution of waiting times between photon emissions as another useful quantity for characterizing photon statistics-in terms of measured quantities, the distribution of waiting times between photoelectrons. By "waiting time" we mean the time T between a photoelectric count recorded at time t, and the next, recorded at time t +T. If photoelectron sequences can be described by a Markov birth process, a single conditional probability density w(~lt) specifies the distribution of waiting times between every pair of photoelectrons. We call this the photoelectron waiting-time distribution. Photoelectron waiting times for coherent light are exponentially distributed.I3 Antibunching implies that photons tend to be separated in time. The distribution of waiting times should then tend to peak around the average time between photoelectric counts. Photoelectron waiting times are certainly not new to

Photoelectron waiting times and atomic state reduction in resonance fluorescence.

Laguerre-Gauss vortex beams carrying different topological charges are generated from Hermite-Gauss laser beams emitted by a gas laser, and their phase properties are explored by studying their interference with a plane wave. Interference of two Laguerre-Gauss vortex beams carrying equal but opposite topological charge is also studied by using a modified Mach-Zehnder interferometer. Experimentally recorded intensity profiles are in good agreement with the theoretically expected profiles.

Phase and interference properties of optical vortex beams

Gaussian beam solutions of Maxwell's equations are constructed in terms of the solutions of the paraxial scalar wave equation. Explicit expressions for the field components of Hermite-Gaussian laser beams are given and their polarization and propagation characteristics are discussed. Experimental evidence for the polarization structure of Hermite-Gaussian laser beams is presented.

Polarization properties of Maxwell-Gaussian laser beams.

Phenolic compounds commonly occurring in fruits, vegetables and tea were studied for their effects on Listeria monocytogenes (L.m.), Escherichia coli O157:H7 (E.c.) and Salmonella Typhimurium (S.T.) in brain–heart infusion broth (BHI) and meat system. Incubated at 37C for 72 h in BHI, gentistic, benzoic and vanillic acids inhibited L.m., E.c and S.T. at 5,000 µg/mL by 2.8 to 3.0 log CFU/mL, 2.8 to 3.0 log CFU/mL and 2.7 to 2.9 log CFU/mL, respectively. Encapsulation of benzoic acid (1,100 µg/mL) in polylactic-co-glycolic acid nanoparticles inhibited 6.5 log CFU/mL of L.m. and S.T., and 6.0 log CFU/mL of E.c. at 48 h. In raw and cooked chicken meat systems, nanoparticle delivery of benzoic acid was effective against S.T. and L.m. (1.0 and 1.6 log CFU/g reduction of S.T. and 1.1 and 3.2 log CFU/g reduction of L.m. compared with 1.2 log CFU/g without nanoparticles on the days 9 and 14 of storage, respectively). These findings demonstrate the efficacy of phenolics on pathogen reduction delivered by nanoparticles and their potential for commercial food safety applications.



PRACTICAL APPLICATIONS

Nanotechnology is an emerging and promising technology that has been advocated for the delivery of antimicrobial phenolic compound extracts to effectively inhibit foodborne pathogens. The method improves the rate of inhibition compared with conventional delivery and retains the antimicrobial efficacy for a longer time. This hurdle technology using natural antimicrobials (phenolic compounds) and nanoparticle-mediated delivery system can effectively decontaminate foodborne pathogens and improve food safety. Phenolic compounds can be used as natural and safer alternatives to chemical disinfectants in food systems and delivered using nanoparticles to better control pathogens for commercial food safety applications.

Enhancement of antimicrobial activities of naturally occurring phenolic compounds by nanoscale delivery against listeria monocytogenes, escherichia coli o157:h7 and salmonella typhimurium in broth and chicken meat system

Surendra Singh

Papers

Field statistics in some generalized Jaynes-Cummings models

Photoelectron waiting times and atomic state reduction in resonance fluorescence.

Phase and interference properties of optical vortex beams

Polarization properties of Maxwell-Gaussian laser beams.

Enhancement of antimicrobial activities of naturally occurring phenolic compounds by nanoscale delivery against listeria monocytogenes, escherichia coli o157:h7 and salmonella typhimurium in broth and chicken meat system