6,453 research outputs found
XUV Free-Electron Laser Experiments on Weakly Bound Dimers: Construction of a Water-Dimer Jet Source and Resonance-Enhanced ICD in Ne<sub>2</sub>
The thesis at hand is dealing with two different experiments on dimers, water (H2O) 2 and Neon dimers Ne2 specifically. The first part focuses on the design and construction of an in-vacuum water cluster source, which operates on the principle of supersonic gas expansion. A subsequent commissioning was done to characterize and optimize the performance of the source with respect to the demanded parameters, especially the water dimer yield. Upcoming experiments on proton transfer dynamics in water dimers will employ the developed cluster source. In the second part, an experiment on the resonance-enhanced Interatomic Coulombic Decay (ICD) is presented. It was carried out at the Free-Electron Laser in Hamburg (FLASH), providing high intensities and photon energies in the extreme ultraviolet regime (XUV). By employing the wavelength tunability of FLASH2, we observed an enhancement of ICD, by scanning the Ne+ (2p) -1 -> Ne+ (2s) -1 resonance at 26:9 eV (46:1nm). The resulting Ne++Ne+ fragments were measured with a Reaction Microscope in coincidence
Laser-Doppler gas-velocity instrument
Three-D instrument using a laser light source measures both turbulence and mean velocity of subsonic and supersonic gas flows. This instrument is based on the measurement of the Doppler frequency shift of light waves scattered by moving particles in the gas stream
Resonators coupled to voltage-biased Josephson junctions: From linear response to strongly driven nonlinear oscillations
Motivated by recent experiments, where a voltage biased Josephson junction is
placed in series with a resonator, the classical dynamics of the circuit is
studied in various domains of parameter space. This problem can be mapped onto
the dissipative motion of a single degree of freedom in a nonlinear
time-dependent potential, where in contrast to conventional settings the
nonlinearity appears in the driving while the static potential is purely
harmonic. For long times the system approaches steady states which are analyzed
in the underdamped regime over the full range of driving parameters including
the fundamental resonance as well as higher and sub-harmonics. Observables such
as the dc-Josephson current and the radiated microwave power give direct
information about the underlying dynamics covering phenomena as bifurcations,
irregular motion, up- and down conversion. Due to their tunability, present and
future set-ups provide versatile platforms to explore the changeover from
linear response to strongly nonlinear behavior in driven dissipative systems
under well defined conditions.Comment: 12 pages, 11 figure
Deconvolution for an atomic distribution: rates of convergence
Let be i.i.d.\ copies of a random variable where and and are independent and have the same
distribution as and respectively. Assume that the random variables
's are unobservable and that where and are independent,
has a Bernoulli distribution with probability of success equal to and
has a distribution function with density Let the random variable
have a known distribution with density Based on a sample
we consider the problem of nonparametric estimation of the
density and the probability Our estimators of and are
constructed via Fourier inversion and kernel smoothing. We derive their
convergence rates over suitable functional classes. By establishing in a number
of cases the lower bounds for estimation of and we show that our
estimators are rate-optimal in these cases.Comment: 27 page
Regulation of cargo transfer between ESCRT-0 and ESCRT-I complexes by flotillin-1 during endosomal sorting of ubiquitinated cargo
Ubiquitin-dependent sorting of membrane proteins in endosomes directs them to lysosomal degradation. In the case of receptors such as the epidermal growth factor receptor (EGFR), lysosomal degradation is important for the regulation of downstream signalling. Ubiquitinated proteins are recognised in endosomes by the endosomal sorting complexes required for transport (ESCRT) complexes, which sequentially interact with the ubiquitinated cargo. Although the role of each ESCRT complex in sorting is well established, it is not clear how the cargo is passed on from one ESCRT to the next. We here show that flotillin-1 is required for EGFR degradation, and that it interacts with the subunits of ESCRT-0 and -I complexes (hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and Tsg101). Flotillin-1 is required for cargo recognition and sorting by ESCRT-0/Hrs and for its interaction with Tsg101. In addition, flotillin-1 is also required for the sorting of human immunodeficiency virus 1 Gag polyprotein, which mimics ESCRT-0 complex during viral assembly. We propose that flotillin-1 functions in cargo transfer between ESCRT-0 and -I complexes
Laser Doppler velocity instrument
Laser Doppler velocity instrument for measuring turbulence and mean velocity in subsonic and supersonic gas flow
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An Engineered Calmodulin-Based Allosteric Switch for Peptide Biosensing
This work describes the development of a new platform for allosteric protein engineering that takes advantage of the ability of calmodulin to change conformation upon binding to peptide and protein ligands. The switch we have developed consists of a fusion protein in which calmodulin is genetically inserted into the sequence of TEM1 β-lactamase. In this approach, calmodulin acts as the input domain, whose ligand-dependent conformational changes control the activity of the β-lactamase output domain. The new allosteric enzyme exhibits up to 120 times higher catalytic activity in the activated (peptide bound) state compared to the inactive (no peptide bound) state in vitro. Activation of the enzyme is ligand-dependent-peptides with higher affinities for wild-type calmodulin exhibit increased switch activity. Calmodulin's ability to "turn on" the activity of β-lactamase makes this a potentially valuable scaffold for the directed evolution of highly specific biosensors for detecting toxins and other clinically relevant biomarkers.Chemistry and Chemical Biolog
Quantum mechanical Carnot engine
A cyclic thermodynamic heat engine runs most efficiently if it is reversible.
Carnot constructed such a reversible heat engine by combining adiabatic and
isothermal processes for a system containing an ideal gas. Here, we present an
example of a cyclic engine based on a single quantum-mechanical particle
confined to a potential well. The efficiency of this engine is shown to equal
the Carnot efficiency because quantum dynamics is reversible. The quantum heat
engine has a cycle consisting of adiabatic and isothermal quantum processes
that are close analogues of the corresponding classical processes.Comment: 10 page
Swimming Efficiency of Bacterium Escherichia Coli
We use in vivo measurements of swimming bacteria in an optical trap to
determine fundamental properties of bacterial propulsion. In particular, we
determine the propulsion matrix, which relates the angular velocity of the
flagellum to the torques and forces propelling the bacterium. From the
propulsion matrix dynamical properties such as forces, torques, swimming speed
and power can be obtained from measurements of the angular velocity of the
motor. We find significant heterogeneities among different individuals even
though all bacteria started from a single colony. The propulsive efficiency,
defined as the ratio of the propulsive power output to the rotary power input
provided by the motors, is found to be 0.2%.Comment: 6 page
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