108 research outputs found
Conductance of electrolytes in 1-propanol solutions from −40 to 25°C
Conductance data for solutions of LiCl, NaBr, NaI, KI, KSCN, RbI, Et4NI, Pr4NI, Bu4NI, Bu4NClO4, n-Am4NI, i-Am4NI, n-Hept4NI, Me2Bu2NI, MeBu3NI, EtBu3NI, i-Am3BuNI, and i-Am3BuNBPh4 in 1-propanol at –40, –30, –20, –10, 0, 10, and 25°C are communicated and discussed. Evaluation of the data is performed on the basis of a conductance equation that includes a term in c3/2. Single ion conductances at 25 and 10°C are determined with the help of transference numbers t o + (KSCN/PrOH); the data are compared to data estimated by other methods. Ion-pair association constants and their temperature dependence are discussed in terms of contact and solvent separated ion pairs, and the role of non-coulombic forces is shown with the help of an appropriate splitting of the Gibbs energy of ion-pair formation
Large optical field enhancement for nanotips with large opening angles
We theoretically investigate the dependence of the enhancement of optical
near-fields at nanometric tips on the shape, size, and material of the tip. We
confirm a strong dependence of the field enhancement factor on the radius of
curvature. In addition, we find a surprisingly strong increase of field
enhancement with increasing opening angle of the nanotips. For gold and
tungsten nanotips in the experimentally relevant parameter range (radius of
curvature nm at nm laser wavelength), we obtain field
enhancement factors of up to for Au and for W for large
opening angles. We confirm this strong dependence on the opening angle for many
other materials featuring a wide variety in their dielectric response. For
dielectrics, the opening angle dependence is traced back to the electrostatic
force of the induced surface charge at the tip shank. For metals, the plasmonic
response strongly increases the field enhancement and shifts the maximum field
enhancement to smaller opening angles.Comment: 16 pages, 12 figure
Information- and Coding-Theoretic Analysis of the RLWE Channel
Several cryptosystems based on the \emph{Ring Learning with Errors} (RLWE)
problem have been proposed within the NIST post-quantum cryptography
standardization process, e.g. NewHope. Furthermore, there are systems like
Kyber which are based on the closely related MLWE assumption. Both previously
mentioned schemes feature a non-zero decryption failure rate (DFR). The
combination of encryption and decryption for these kinds of algorithms can be
interpreted as data transmission over noisy channels. To the best of our
knowledge this paper is the first work that analyzes the capacity of this
channel. We show how to modify the encryption schemes such that the input
alphabets of the corresponding channels are increased. In particular, we
present lower bounds on their capacities which show that the transmission rate
can be significantly increased compared to standard proposals in the
literature. Furthermore, under the common assumption of stochastically
independent coefficient failures, we give lower bounds on achievable rates
based on both the Gilbert-Varshamov bound and concrete code constructions using
BCH codes. By means of our constructions, we can either increase the total
bitrate (by a factor of for Kyber and by factor of for NewHope)
while guaranteeing the same \emph{decryption failure rate} (DFR). Moreover, for
the same bitrate, we can significantly reduce the DFR for all schemes
considered in this work (e.g., for NewHope from to ).Comment: 13 pages, 4 figures, 3 table
Controlling ultrafast currents by the non-linear photogalvanic effect
We theoretically investigate the effect of broken inversion symmetry on the
generation and control of ultrafast currents in a transparent dielectric (SiO2)
by strong femto-second optical laser pulses. Ab-initio simulations based on
time-dependent density functional theory predict ultrafast DC currents that can
be viewed as a non-linear photogalvanic effect. Most surprisingly, the
direction of the current undergoes a sudden reversal above a critical threshold
value of laser intensity I_c ~ 3.8*10^13 W/cm2. We trace this switching to the
transition from non-linear polarization currents to the tunneling excitation
regime. We demonstrate control of the ultrafast currents by the time delay
between two laser pulses. We find the ultrafast current control by the
non-linear photogalvanic effect to be remarkably robust and insensitive to
laser-pulse shape and carrier-envelope phase
2 kirja A. de Vignolles`ile, Berlin
http://tartu.ester.ee/record=b1890571~S1*es
Ab-initio multi-scale simulation of high-harmonic generation in solids
High-harmonic generation by a highly non-linear interaction of infrared laser
fields with matter allows for the generation of attosecond pulses in the XUV
spectral regime. This process, well established for atoms, has been recently
extended to the condensed phase. Remarkably well pronounced harmonics up to
order ~30 have been observed for dielectrics. We present the first ab-initio
multi-scale simulation of solid-state high-harmonic generation. We find that
mesoscopic effects of the extended system, in particular the realistic sampling
of the entire Brillouin zone, the pulse propagation in the dense medium, and
the inhomogeneous illumination of the crystal have a strong effect on the
formation of clean harmonic spectra. Our results provide a novel explanation
for the formation of clean harmonics and have implications for a wide range of
non-linear optical processes in dense media
Nanoparticle detection in an open-access silicon microcavity
We report on the detection of free nanoparticles in a micromachined,
open-access Fabry-P\'erot microcavity. With a mirror separation of m,
a radius of curvature of mm, and a beam waist of m, the mode
volume of our symmetric infrared cavity is smaller than pL. The small
beam waist, together with a finesse exceeding 34,000, enables the detection of
nano-scale dielectric particles in high vacuum. This device allows monitoring
of the motion of individual nm radius silica nanospheres in real time.
We observe strong coupling between the particles and the cavity field, a
precondition for optomechanical control. We discuss the prospects for optical
cooling and detection of dielectric particles smaller than nm in radius
and amu in mass.Comment: 4 pages, 3 figure
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