Experimental demonstration of the stability of Berry's phase for a spin-1/2 particle

The geometric phase has been proposed as a candidate for noise resilient coherent manipulation of fragile quantum systems. Since it is determined only by the path of the quantum state, the presence of noise fluctuations affects the geometric phase in a different way than the dynamical phase. We have experimentally tested the robustness of Berry's geometric phase for spin-1/2 particles in a cyclically varying magnetic field. Using trapped polarized ultra-cold neutrons it is demonstrated that the geometric phase contributions to dephasing due to adiabatic field fluctuations vanish for long evolution times.Comment: 4 pages, 4 figure

Daily Eastern News: November 10, 1975

https://thekeep.eiu.edu/den_1975_nov/1005/thumbnail.jp

Insertion of T4-lysozyme (T4L) can be a useful tool for studying olfactory-related GPCRs.

The detergents used to solubilize GPCRs can make crystal growth the rate-limiting step in determining their structure. The Kobilka laboratory showed that insertion of T4-lysozyme (T4L) in the 3rd intracellular loop is a promising strategy towards increasing the solvent-exposed receptor area, and hence the number of possible lattice-forming contacts. The potential to use T4L with the olfactory-related receptors hOR17-4 and hVN1R1 was thus tested. The structure and function of native and T4L-variants were compared. Both receptors localized to the cell membrane, and could initiate ligand-activated signaling. Purified receptors not only had the predicted alpha-helical structures, but also bound their ligands canthoxal (MW = 178.23) and myrtenal (MW = 150.22). Interestingly, the T4L variants had higher percentages of soluble monomers compared to protein aggregates, effectively increasing the protein yield that could be used for structural and function studies. They also bound their ligands for longer times, suggesting higher receptor stability. Our results indicate that a T4L insertion may be a general method for obtaining GPCRs suitable for structural studies

An Improved Search for the Neutron Electric Dipole Moment

A permanent electric dipole moment of fundamental spin-1/2 particles violates both parity (P) and time re- versal (T) symmetry, and hence, also charge-parity (CP) symmetry since there is no sign of CPT-violation. The search for a neutron electric dipole moment (nEDM) probes CP violation within and beyond the Stan- dard Model. The experiment, set up at the Paul Scherrer Institute (PSI), an improved, upgraded version of the apparatus which provided the current best experimental limit, dn < 2.9E-26 ecm (90% C.L.), by the RAL/Sussex/ILL collaboration: Baker et al., Phys. Rev. Lett. 97, 131801 (2006). In the next two years we aim to improve the sensitivity of the apparatus to sigma(dn) = 2.6E-27 ecm corresponding to an upper limit of dn < 5E-27 ecm (95% C.L.), in case for a null result. In parallel the collaboration works on the design of a new apparatus to further increase the sensitivity to sigma(dn) = 2.6E-28 ecm.Comment: APS Division for particles and fields, Conference Proceedings, Two figure

Improving the performance of aeroacoustic measurements beneath a turbulent boundary layer in a wake flow

Experimental measurement and subsequent numerical prediction of the excitation of at plates or car windows beneath a turbulent boundary layer have become important for the development of novel cars and airplanes. A wavenumber spectrum can be used to define the load on a plat caused by the pressure fluctuations on the surface. Wavenumber spectra from measurements are used to validate the numerical predictions of the acoustic and hydrodynamic portions of the pressure fluctuations. When measuring wavenumber spectra, the design of the experiment can have a large in fluence on the outcome. In this paper, the effects of both array design and the application of deconvolution algorithms on the experimental determination of the wavenumber-frequency spectrum are evaluated

Gravitational depolarization of ultracold neutrons: comparison with data

We compare the expected effects of so-called gravitationally enhanced depolarization of ultracold neutrons to measurements carried out in a spin-precession chamber exposed to a variety of vertical magnetic-field gradients. In particular, we have investigated the dependence upon these field gradients of spin-depolarization rates and also of shifts in the measured neutron Larmor precession frequency. We find excellent qualitative agreement, with gravitationally enhanced depolarization accounting for several previously unexplained features in the data

Membrane permeation of arginine-rich cell-penetrating peptides independent of transmembrane potential as a function of lipid composition and membrane fluidity

Cell-penetrating peptides (CPPs) are prominent delivery vehicles to confer cellular entry of (bio-) macromolecules. Internalization efficiency and uptake mechanism depend, next to the type of CPP and cargo, also on cell type. Direct penetration of the plasma membrane is the preferred route of entry as this circumvents endolysosomal sequestration. However, the molecular parameters underlying this import mechanism are still poorly defined. Here, we make use of the frequently used HeLa and HEK cell lines to address the role of lipid composition and membrane potential. In HeLa cells, at low concentrations, the CPP nona-arginine (R9) enters cells by endocytosis. Direct membrane penetration occurs only at high peptide concentrations through a mechanism involving activation of sphingomyelinase which converts sphingomyelin into ceramide. In HEK cells, by comparison, R9 enters the cytoplasm through direct membrane permeation already at low concentrations. This direct permeation is strongly reduced at room temperature and upon cholesterol depletion, indicating a complex dependence on membrane fluidity and microdomain organisation. Lipidomic analyses show that in comparison to HeLa cells HEK cells have an endogenously low sphingomyelin content. Interestingly, direct permeation in HEK cells and also in HeLa cells treated with exogenous sphingomyelinase is independent of membrane potential. Membrane potential is only required for induction of sphingomyelinase-dependent uptake which is then associated with a strong hyperpolarization of membrane potential as shown by whole-cell patch clamp recordings. Next to providing new insights into the interplay of membrane composition and direct permeation, these results also refute the long-standing paradigm that transmembrane potential is a driving force for CPP uptake

Diffraction of slow neutrons by holographic SiO_2 nanoparticle-polymer composite gratings

Diffraction experiments with holographic gratings recorded in SiO$_2$ nanoparticle-polymer composites have been carried out with slow neutrons. The influence of parameters such as nanoparticle concentration, grating thickness and grating spacing on the neutron-optical properties of such materials has been tested. Decay of the grating structure along the sample depth due to disturbance of the recording process becomes an issue at grating thicknesses of about 100 microns and larger. This limits the achievable diffraction efficiency for neutrons. As a solution to this problem, the Pendell\"{o}sung interference effect in holographic gratings has been exploited to reach a diffraction efficiency of 83% for very cold neutrons.Comment: 7 pages, 3 figures, submitted to Phys. Rev.

An Improved Neutron Electric Dipole Moment Experiment

A new measurement of the neutron EDM, using Ramsey's method of separated oscillatory fields, is in preparation at the new high intensity source of ultra-cold neutrons (UCN) at the Paul Scherrer Institute, Villigen, Switzerland (PSI). The existence of a non-zero nEDM would violate both parity and time reversal symmetry and, given the CPT theorem, might lead to a discovery of new CP violating mechanisms. Already the current upper limit for the nEDM (|d_n|<2.9E-26 e.cm) constrains some extensions of the Standard Model. The new experiment aims at a two orders of magnitude reduction of the experimental uncertainty, to be achieved mainly by (1) the higher UCN flux provided by the new PSI source, (2) better magnetic field control with improved magnetometry and (3) a double chamber configuration with opposite electric field directions. The first stage of the experiment will use an upgrade of the RAL/Sussex/ILL group's apparatus (which has produced the current best result) moved from Institut Laue-Langevin to PSI. The final accuracy will be achieved in a further step with a new spectrometer, presently in the design phase.Comment: Flavor Physics & CP Violation Conference, Taipei, 200

Synchronous Infra-Slow Oscillations Organize Ensembles of Accessory Olfactory Bulb Projection Neurons into Distinct Microcircuits

The accessory olfactory system controls social and sexual behavior. In the mouse accessory olfactory bulb, the first central stage of information processing along the accessory olfactory pathway, projection neurons (mitral cells) display infra-slow oscillatory discharge with remarkable periodicity. The physiological mechanisms that underlie this default output state, however, remain controversial. Moreover, whether such rhythmic infra-slow activity patterns exist in awake behaving mice and whether such activity reflects the functional organization of the accessory olfactory bulb circuitry remain unclear. Here, we hypothesize that mitral cell ensembles form synchronized microcircuits that subdivide the accessory olfactory bulb into segregated functional clusters. We use a miniature microscope to image the Ca2+ dynamics within the apical dendritic compartments of large mitral cell ensembles in vivo. We show that infra-slow periodic patterns of concerted neural activity, indeed, reflect the idle state of accessory olfactory bulb output in awake male and female mice. Ca2+ activity profiles are distinct and glomerulus-specific. Confocal time-lapse imaging in acute slices reveals that groups of mitral cells assemble into microcircuits that exhibit correlated Ca2+ signals. Moreover, electrophysiological profiling of synaptic connectivity indicates functional coupling between mitral cells. Our results suggest that both intrinsically rhythmogenic neurons and neurons entrained by fast synaptic drive are key elements in organizing the accessory olfactory bulb into functional microcircuits, each characterized by a distinct default pattern of infra-slow rhythmicity