Four wave mixing with self-phase matching due to collective atomic recoil

We describe a method for non-degenerate four-wave mixing in a cold sample of 4-level atoms. An integral part of the four-wave mixing process is a collective instability which spontaneously generates a periodic density modulation in the cold atomic sample with a period equal to half of the wavelength of the generated high-frequency optical field. Due to the generation of this density modulation, phase-matching between the pump and scattered fields is not a necessary initial condition for this wave-mixing process to occur, rather the density modulation acts to "self phase-match" the fields during the course of the wave-mixing process. We describe a one-dimensional model of this process, and suggest a proof-of-principle experiment which would involve pumping a sample of cold Cs atoms with three infra-red pump fields to produce blue light.Comment: to appear in Physical Review Letter

Inducing strong density modulation with small energy dispersion in particle beams and the harmonic amplifier free electron laser

We present a possible method of inducing a periodic density modulation in a particle beam with little increase in the energy dispersion of the particles. The flow of particles in phase space does not obey Liouville's Theorem. The method relies upon the Kuramoto-like model of collective synchronism found in free electron generators of radiation, such as Cyclotron Resonance Masers and the Free Electron Laser. For the case of an FEL interaction, electrons initially begin to bunch and emit radiation energy with a correlated energy dispersion which is periodic with the FEL ponderomotive potential. The relative phase between potential and particles is then changed by approximately 180 degrees. The particles continue to bunch, however, there is now a correlated re-absorption of energy from the field. We show that, by repeating this relative phase change many times, a significant density modulation of the particles may be achieved with only relatively small energy dispersion. A similar method of repeated relative electron/radiation phase changes is used to demonstrate supression of the fundamental growth in a high gain FEL so that the FEL lases at the harmonic only

Investigation of Substituted-Benzene Dopants for Charge Exchange Ionization of Nonpolar Compounds by Atmospheric Pressure Photoionization

Atmospheric pressure photoionization (APPI) using a dopant enables both polar and nonpolar compounds to be analyzed by LC/MS. To date, the charge exchange ionization pathway utilized for nonpolar compounds has only been efficient under restrictive conditions, mainly because the usual charge exchange reagent ions—the dopant photoions themselves—tend to be consumed in proton transfer reactions with solvent and/or dopant neutrals. This research aims to elucidate the factors affecting the reactivities of substituted-benzene dopant ions; another, overriding, objective is to discover new dopants for better implementing charge exchange ionization in reversed-phase LC/MS applications. The desirable properties for a charge exchange dopant include low reactivity of its photoions with solvent and dopant neutrals and high ionization energy (IE). Reactivity tests were performed for diverse substituted-benzene compounds, with substituents ranging from strongly electron withdrawing (EW) to strongly electron donating (ED). The results indicate that both the tendency of a dopant's photoions to be lost through proton transfer reactions and its IE depend on the electron donating/withdrawing properties of its substituent(s): ED groups decrease reactivity and IE, while EW groups increase reactivity and IE. Exceptions to the reactivity trend for dopants with ED groups occur when the substituent is itself acidic. All told, the desirable properties for a charge exchange dopant tend towards mutual exclusivity. Of the singly-substituted benzenes tested, chloro- and bromobenzene provide the best compromise between low reactivity and high IE. Several fluoroanisoles, with counteracting EW and ED groups, may also provide improved performance relative to the established dopants

The role of quantum fluctuations in the optomechanical properties of a Bose-Einstein condensate in a ring cavity

We analyze a detailed model of a Bose-Einstein condensate trapped in a ring optical resonator and contrast its classical and quantum properties to those of a Fabry-P{\'e}rot geometry. The inclusion of two counter-propagating light fields and three matter field modes leads to important differences between the two situations. Specifically, we identify an experimentally realizable region where the system's behavior differs strongly from that of a BEC in a Fabry-P\'{e}rot cavity, and also where quantum corrections become significant. The classical dynamics are rich, and near bifurcation points in the mean-field classical system, the quantum fluctuations have a major impact on the system's dynamics.Comment: 11 pages, 11 figures, submitted to PR

Preparing students to be doctors: introduction of a sub-internship program.

Preparing graduates for the transformation from medical student to doctor provides medical schools with a real challenge. Medical educators advocate a process of graduated delegation of responsibility in the clinical years of medical school. This is best exemplified in the North American system of sub-internship programmes; an educational approach which European medical schools have been slow to adopt. This study reports on the introduction of an intensive two-week surgical sub-internship for final medical year students. \u22Sub-interns\u22 were asked to complete pre and post sub-internship online questionnaires assessing their readiness to perform clinical and practical skills, attitudes towards the program, and how well it prepared students for internship. Forty-nine students completed a questionnaire pre sub-internship and 47 completed the post-questionnaire. Student confidence towards practical and clinical skills and their first day at work increased over the two weeks. Mean Iikert scores for all 6 practical and clinical skills improved post sub-internship. The introduction of a surgical sub-internship is timely and welcomed by medical students. Its development helps bridge the gap in responsibilities between medical student and doctor

Recoil-induced effects in passive and active atomic systems

Abstract A theoretical analysis of absorptive optical bistability in a passive atomic medium and bidirectional lasing in an active atomic medium is presented. The atomic medium consists of a collection of cold two-level atoms and the atom-radiation field interaction is described using a one-dimensional semiclassical model. It is shown that when the effects of atomic recoil are included self-consistently, the interaction between the atoms and the radiation can be changed significantly from that when the effects of atomic recoil are neglected.

Divergent Mitochondrial Biogenesis Responses in Human Cardiomyopathy

Background—Mitochondria are key players in the development and progression of heart failure (HF). Mitochondrial (mt) dysfunction leads to diminished energy production and increased cell death contributing to the progression of left ventricular failure. The fundamental mechanisms that underlie mt dysfunction in HF have not been fully elucidated. Methods and Results—To characterize mt morphology, biogenesis, and genomic integrity in human HF, we investigated left ventricular tissue from nonfailing hearts and end-stage ischemic (ICM) or dilated (DCM) cardiomyopathic hearts. Although mt dysfunction was present in both types of cardiomyopathy, mt were smaller and increased in number in DCM compared with ICM or nonfailing hearts. mt volume density and mtDNA copy number was increased by ≈2-fold (P<0.001) in DCM hearts in comparison with ICM hearts. These changes were accompanied by an increase in the expression of mtDNA-encoded genes in DCM versus no change in ICM. mtDNA repair and antioxidant genes were reduced in failing hearts, suggestive of a defective repair and protection system, which may account for the 4.1-fold increase in mtDNA deletion mutations in DCM (P<0.05 versus nonfailing hearts, P<0.05 versus ICM). Conclusions—In DCM, mt dysfunction is associated with mtDNA damage and deletions, which could be a consequence of mutating stress coupled with a peroxisome proliferator-activated receptor γ coactivator 1α–dependent stimulus for mt biogenesis. However, this maladaptive compensatory response contributes to additional oxidative damage. Thus, our findings support further investigations into novel mechanisms and therapeutic strategies for mt dysfunction in DCM