Calculation of cyclotron resonance linewidth due to ionized impurities and longitudinal optical phonons

The cyclotron resonance linewidth for free carriers in semiconductors is calculated, starting from the Kubo formula. Ionized impurity and LO phonon scattering are taken into account. The absorption spectrum is investigated in the Relaxation Kernel approach and the scattering is treated in the lowest order Born approximation. For T>15 K, excellent agreement is obtained with the measurements of Matsuda et al. in InSb. No adjustable parameters are introduced.     

The energy loss function of the polaron gas

The energy loss function Im 1/K(π, ω) of a gas of polarons is calculated in the RPA approximation. For typical densities of degenerate polar semiconductors, the energy loss function has pronounced structure. Up to three resonances appear. The coupled phonon-plasmon resonance, with frequency between ω_TO and ω_LO, leads to an extremely sharp peak in Im 1/K(π, ω), for appropriate values of wavevector and densities.     

Discontinuous behaviour of a polaron in a high magnetic field at non-zero temperature

The results reported recently concerning the phase transition of a polaron in a high magnetic field at zero temperature are generalized to arbitrary temperature. An experiment to observe this polaron phase-transition is suggested and the relevant parameters are given for sixteen compound semiconductors.     

A conceptual difficulty with the distribution function for polarons,linearized in the electric field

The steady state limit of Boltzmann's equation for a polaron at weak electron-phonon coupling is studied in the ohmic regime. It is shown that the linearization of the distribution function to first order in the electric field, even at arbitrarily small field, necessarily leads to a negative distribution in some region of momentum space, if a Maxwellian distribution is assumed at zero field.     

Theoretical evidence for the possible observation of relaxed excited states of Fröhlich polarons for polar crystals with α > 3.

The optical absorption spectrum of Fröhlich polarons has been calculated for the first time for arbitrary electron-phonon interaction     

Application of MALDI-TOF mass spectrometry for the detection of enterotoxins produced by pathogenic strains of the Bacillus cereus group

Enterotoxins produced by different species of the Bacillus cereus group, such as cytotoxin K1 (CytK1) and non-haemolytic enterotoxin (NHE), have been associated with diarrhoeal food poisoning incidents. Detection of CytK1 is not possible with commercial assays while NHE is recognised by an immunological kit (TECRA) that does not specifically target this protein because it is based on polyclonal antibodies. It is evident that the lack of suitable tools for the study of enterotoxins hampers the possibilities for accurate hazard identification and characterisation in microbial food safety risk assessment. We applied matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS) for the detection of CytK1 and NHE produced by pathogenic strains of the B. cereus group using protein digests from 1D gel electrophoresis. Secretion of CytK1 and two of the three components of NHE was confirmed in supernatants of different B. cereus cultures. For each protein, we introduce biomarkers that could be used for the screening of food poisoning or food/environmental isolates that can secrete enterotoxins. For example, tryptic peptides of 2,310.2 and 1,192.5?Da (calculated mass) can be indicators for CytK1 and NheA, respectively, although a simultaneous detection of other enterotoxin-specific peptides is recommended to assure the presence of a toxin in an unknown sample. Comparison of MALDI-TOF/MS with the TECRA kit showed that our methodological strategy performed well and it had the competitive advantage of specifically detecting NheA. Therefore, MALDI-TOF/MS can be successfully incorporated into risk assessment procedures in order to determine the involvement of strains of the B. cereus group in foodborne outbreaks, including the recently described cytK1 producing species, Bacillus cytotoxicus.     

Population imbalance as a vortex catalyst in Fermi superfluids

Pairing leads to superfluidity in ultracold atomic gases, but this pairing can be frustrated when a population imbalance is present between the pairing partners. Here we investigate how vortices in the fermionic superfluid are affected by imbalance. We show that the vortex core radius is increased by imbalance, accommodating excess component atoms. This has two intriguing consequences. Firstly, a small imbalance acts as a catalyst for vortex formation, decreasing the critical rotation frequency. Secondly, imbalanced gases near critical imbalance can exhibit rotationally induced superfluidity.     

Coupled ripplon-plasmon modes in a multielectron bubble

In multielectron bubbles, the electrons form an effectively two-dimensional layer at the inner surface of the bubble in helium. The modes of oscillation of the bubble surface (the ripplons) are influenced by the charge redistribution of the electrons along the surface. The dispersion relation for these charge redistribution modes (‘longitudinal plasmons’) is derived and the coupling of these modes to the ripplons is analysed. We find that the ripplon-plasmon coupling in a multielectron bubble differs markedly from that of electrons on a flat helium surface. An equation is presented relating the spherical harmonic components of the charge redistribution to those of the shape deformation of the bubble.