6,547 research outputs found
Atom Transfer and Single-Adatom Contacts
The point contact of a tunnel tip approaching towards Ag(111) and Cu(111)
surfaces is investigated with a low temperature scanning tunneling microscope.
A sharp jump-to-contact, random in nature, is observed in the conductance.
After point contact, the tip-apex atom is transferred to the surface,
indicating that a one-atom contact is formed during the approach. In sharp
contrast, the conductance over single silver and copper adatoms exhibits a
smooth and reproducible transition from tunneling to contact regime. Numerical
simulations show that this is a consequence of the additional dipolar bonding
between the homoepitaxial adatom and the surface atoms.Comment: 4 pages, 4 figure
Studies of a weak polyampholyte at the air-buffer interface: The effect of varying pH and ionic strength
We have carried out experiments to probe the static and dynamic interfacial
properties of --casein monolayers spread at the air-buffer interface,
and analysed these results in the context of models of weak polyampholytes.
Measurements have been made systematically over a wide range of ionic strength
and pH. In the semi-dilute regime of surface concentration a scaling exponent,
which can be linked to the degree of chain swelling, is found. This shows that
at pH close to the isoelectric point, the protein is compact. At pH away from
the isoelectric pH the protein is extended. The transition between compact and
extended states is continuous. As a function of increasing ionic strength, we
observe swelling of the protein at the isoelectric pH but contraction of the
protein at pH values away from it. These behaviours are typical of a those
predicted theoretically for a weak polyampholyte. Dilational moduli
measurements, made as a function of surface concentration exhibit maxima that
are linked to the collapse of hydrophilic regions of the protein into the
subphase. Based on this data we present a configuration map of the protein
configuration in the monolayer. These findings are supported by strain (surface
pressure) relaxation measurements and surface quasi-elastic light scattering
(SQELS) measurements which suggest the existence of loops and tails in the
subphase at higher surface concentrations.Comment: Submitted to J. Chem. Phy
Creating pseudo Kondo-resonances by field-induced diffusion of atomic hydrogen
In low temperature scanning tunneling microscopy (STM) experiments a cerium
adatom on Ag(100) possesses two discrete states with significantly different
apparent heights. These atomic switches also exhibit a Kondo-like feature in
spectroscopy experiments. By extensive theoretical simulations we find that
this behavior is due to diffusion of hydrogen from the surface onto the Ce
adatom in the presence of the STM tip field. The cerium adatom possesses
vibrational modes of very low energy (3-4meV) and very high efficiency (> 20%),
which are due to the large changes of Ce-states in the presence of hydrogen.
The atomic vibrations lead to a Kondo-like feature at very low bias voltages.
We predict that the same low-frequency/high-efficiency modes can also be
observed at lanthanum adatoms.Comment: five pages and four figure
Discovery of dumbbell-shaped Cs*He_n exciplexes in solid He 4
We have observed several new spectral features in the fluorescence of cesium
atoms implanted in the hcp phase of solid helium following laser excitation to
the 6P states. Based on calculations of the emission spectra using
semiempirical Cs-He pair potentials the newly discovered lines can be assigned
to the decay of specific Cs*He exciplexes: an apple-shaped CsHe and a dumbbell-shaped CsHe exciplex with
a well defined number of bound helium atoms. While the former has been
observed in other enviroments, it was commonly believed that exciplexes with
might not exist. The calculations suggest CsHe to be
the most probable candidate for that exciplex, in which the helium atoms are
arranged on a ring around the waist of the dumbbell shaped electronic density
distribution of the cesium atom.Comment: 4 pages, 4 figure
Causation, Measurement Relevance and No-conspiracy in EPR
In this paper I assess the adequacy of no-conspiracy conditions employed in
the usual derivations of the Bell inequality in the context of EPR
correlations. First, I look at the EPR correlations from a purely
phenomenological point of view and claim that common cause explanations of
these cannot be ruled out. I argue that an appropriate common cause explanation
requires that no-conspiracy conditions are re-interpreted as mere common
cause-measurement independence conditions. In the right circumstances then,
violations of measurement independence need not entail any kind of conspiracy
(nor backwards in time causation). To the contrary, if measurement operations
in the EPR context are taken to be causally relevant in a specific way to the
experiment outcomes, their explicit causal role provides the grounds for a
common cause explanation of the corresponding correlations.Comment: 20 pages, 1 figur
Quantum Rotor Engines
This chapter presents autonomous quantum engines that generate work in the
form of directed motion for a rotor. We first formulate a prototypical
clock-driven model in a time-dependent framework and demonstrate how it can be
translated into an autonomous engine with the introduction of a planar rotor
degree of freedom. The rotor plays both the roles of internal engine clock and
of work repository. Using the example of a single-qubit piston engine, the
thermodynamic performance is then reviewed. We evaluate the extractable work in
terms of ergotropy, the kinetic energy associated to net directed rotation, as
well as the intrinsic work based on the exerted torque under autonomous
operation; and we compare them with the actual energy output to an external
dissipative load. The chapter closes with a quantum-classical comparison of the
engine's dynamics. For the single-qubit piston example, we propose two
alternative representations of the qubit in an entirely classical framework:
(i) a coin flip model and (ii) a classical magnet moment, showing subtle
differences between the quantum and classical descriptions.Comment: Chapter of the upcoming book "Thermodynamics in the Quantum Regime -
Recent Progress and Outlook
PrĂ€operative NĂŒchternzeiten: Sicht der Patienten
Zusammenfassung: Hintergrund: Mit dem Ziel der subjektiven perioperativen QualitĂ€tsverbesserung scheint es wĂŒnschenswert, die prĂ€operativen NĂŒchternzeiten im Rahmen der als sicher geltenden Grenzen so kurz als möglich zu halten. Diese MaĂnahmen sollten mit einer messbaren Verminderung von prĂ€operativem Hunger und Durst einhergehen und v.a. in einer Verbesserung der prĂ€operativen Befindlichkeit resultieren. Welchen Einfluss Durst und Hunger aus Patientensicht auf den prĂ€operativen Komfort haben, ist jedoch weit gehend unbekannt. Ziel dieser Studie war es, das AusmaĂ der BeeintrĂ€chtigung der Patienten durch eine traditionelle NĂŒchternheitsregelung abzuschĂ€tzen. Patienten und Methoden: Ein Kollektiv von 412Patienten der "American-Society-of-Anesthesiologists"- (ASA-)RisikoklassenI und II, das sich einem kleineren chirurgischen Eingriff unterzog, wurde mithilfe eines Fragebogens zum AusmaĂ und Stellenwert von prĂ€operativem Durst und Hunger befragt. Ergebnisse: Es hatten 33% der Patienten mĂ€Ăigen oder starken Durst, 19% mĂ€Ăigen bis starken Hunger. Von den Befragten möchten 47% vor der Operation noch trinken, 72% hĂ€tten gern noch ein leichtes FrĂŒhstĂŒck eingenommen. Die mittlere NĂŒchternzeit war 12,8±3,4h fĂŒr FlĂŒssigkeiten und 15,5±4,4h fĂŒr Essen. Durst wurde von 3,3% und Hunger von 0,8% der Patienten als Hauptgrund fĂŒr die BeeintrĂ€chtigung des prĂ€operativen Wohlbefindens genannt. Das lange Warten (8,5%), NervositĂ€t (6,5%) und Angst (4,8%) wurden am hĂ€ufigsten genannt. Die Antworten waren unabhĂ€ngig von der Zeitdauer der prĂ€operativen NĂŒchternheit. Schlussfolgerung: Der Patientenkomfort ist durch eine traditionelle NĂŒchternheitsregelung beeintrĂ€chtigt, und Minimierung der prĂ€operativen NĂŒchternzeiten wird von den Patienten gewĂŒnscht. Anstrengungen mit dem Ziel der Reduktion von prĂ€operativer Angst und NervositĂ€t bergen jedoch zusĂ€tzliches groĂes Potenzial fĂŒr eine Steigerung der perioperativen BehandlungsqualitĂ€t aus Sicht der Patiente
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