11,741 research outputs found
Surface Percolation and Growth. An alternative scheme for breaking the diffraction limit in optical patterning
A nanopatterning scheme is presented by which the structure height can be
controlled in the tens of nanometers range and the lateral resolution is a
factor at least three times better than the point spread function of the
writing beam. The method relies on the initiation of the polymerization
mediated by a very inefficient energy transfer from a fluorescent dye molecule
after single photon absorption. The mechanism has the following distinctive
steps: the dye adsorbs on the substrate surface with a higher concentration
than in the bulk, upon illumination it triggers the polymerization, then
isolated islands develop and merge into a uniform structure (percolation),
which subsequently grows until the illumination is interrupted. This
percolation mechanism has a threshold that introduces the needed nonlinearity
for the fabrication of structures beyond the diffraction limit.Comment: 10 pages, 8 figure
Linearization of nonlinear connections on vector and affine bundles, and some applications
A linear connection is associated to a nonlinear connection on a vector
bundle by a linearization procedure. Our definition is intrinsic in terms of
vector fields on the bundle. For a connection on an affine bundle our procedure
can be applied after homogenization and restriction. Several applications in
Classical Mechanics are provided
Revolving rivers in sandpiles: from continuous to intermittent flows
In a previous paper [Phys. Rev. Lett. 91, 014501 (2003)], the mechanism of
"revolving rivers" for sandpile formation is reported: as a steady stream of
dry sand is poured onto a horizontal surface, a pile forms which has a river of
sand on one side owing from the apex of the pile to the edge of the base. For
small piles the river is steady, or continuous. For larger piles, it becomes
intermittent. In this paper we establish experimentally the "dynamical phase
diagram" of the continuous and intermittent regimes, and give further details
of the piles topography, improving the previous kinematic model to describe it
and shedding further light on the mechanisms of river formation. Based on
experiments in Hele-Shaw cells, we also propose that a simple dimensionality
reduction argument can explain the transition between the continuous and
intermittent dynamics.Comment: 8 pages, 11 figures, submitted to Phys Rev
Experimental determination of distance and orientation of metallic nanodimers by polarization dependent plasmon coupling
Live cell imaging using metallic nanoparticles as tags is an emerging
technique to visualize long and highly dynamic processes due to the lack of
photobleaching and high photon rate. However, the lack of excited states as
compared to fluorescent dyes prevents the use of resonance energy transfer and
recently developed super resolution methods to measure distances between
objects closer that the resolution limit. In this work, we experimentally
demonstrate a technique to determine subdiffraction distances based on the near
field coupling of metallic nanoparticles. Due to the symmetry breaking in the
scattering cross section, not only distances but also relative orientations can
be measured. Gold nanoparticles were prepared on glass in such way that a small
fraction of dimers was present. The sample was sequentially illuminated with
two wavelengths to separate background from nanoparticle scattering based on
their spectral properties. A novel total internal reflection illumination
scheme in which the polarization can be rotated was used to further minimize
background contributions. In this way, radii, distance and orientation were
measured for each individual dimer and their statistical distributions were
found to be in agreement with the expected ones. We envision that this
technique will allow fast and long term tracking of relative distance and
orientation in biological processes.Comment: 9 pages, 5 figures, Commentary from the reviewer available in Papers
in Physic
Trustee: Full Privacy Preserving Vickrey Auction on top of Ethereum
The wide deployment of tokens for digital assets on top of Ethereum implies
the need for powerful trading platforms. Vickrey auctions have been known to
determine the real market price of items as bidders are motivated to submit
their own monetary valuations without leaking their information to the
competitors. Recent constructions have utilized various cryptographic protocols
such as ZKP and MPC, however, these approaches either are partially
privacy-preserving or require complex computations with several rounds. In this
paper, we overcome these limits by presenting Trustee as a Vickrey auction on
Ethereum which fully preserves bids' privacy at relatively much lower fees.
Trustee consists of three components: a front-end smart contract deployed on
Ethereum, an Intel SGX enclave, and a relay to redirect messages between them.
Initially, the enclave generates an Ethereum account and ECDH key-pair.
Subsequently, the relay publishes the account's address and ECDH public key on
the smart contract. As a prerequisite, bidders are encouraged to verify the
authenticity and security of Trustee by using the SGX remote attestation
service. To participate in the auction, bidders utilize the ECDH public key to
encrypt their bids and submit them to the smart contract. Once the bidding
interval is closed, the relay retrieves the encrypted bids and feeds them to
the enclave that autonomously generates a signed transaction indicating the
auction winner. Finally, the relay submits the transaction to the smart
contract which verifies the transaction's authenticity and the parameters'
consistency before accepting the claimed auction winner. As part of our
contributions, we have made a prototype for Trustee available on Github for the
community to review and inspect it. Additionally, we analyze the security
features of Trustee and report on the transactions' gas cost incurred on
Trustee smart contract.Comment: Presented at Financial Cryptography and Data Security 2019, 3rd
Workshop on Trusted Smart Contract
Angular emission properties of a layer of rare-earth based nanophosphors embedded in one-dimensional photonic crystal coatings
The angular properties of light emitted from rare-earth based nanophosphors embedded in optical resonators built in one-dimensional photonic crystal coatings are herein investigated. Strong directional dependence of the photoluminescence spectra is found. Abrupt angular variations of the enhancement caused by the photonic structure and the extraction power are observed, in good agreement with calculated polar emission patterns. Our results confirm that the optical cavity favors the extraction of different wavelengths at different angles and that integration of nanophosphors within photonic crystals provides control over the directional emission properties that could be put into practice in phosphorescent displays.Ministerio de Ciencia e Innovación MAT2008- 02166, CSD2007-00007Junta de Andalucía FQM3579, FQM524
Phase diagram of silicon from atomistic simulations
In this letter we present a calculation of the temperature-pressure phase
diagram of Si in a range of pressures covering from -5 to 20 GPa and
temperatures up to the melting point. The phase boundaries and triple points
between the diamond, liquid, -Sn and clathrate phases are
reported. We have employed efficient simulation techniques to calculate free
energies and to numerically integrate the Clausius-Clapeyron equation, combined
with a tight binding model capable of an accuracy comparable to that of
first-principles methods. The resulting phase diagram agrees well with the
available experimental data.Comment: 5 pages, 1 figure, accepted in PR
Análisis de la uniformidad de riego en sistemas de aspersión semiportátil con aspersores de gran tamaño
La sostenibilidad en la agricultura de regadío depende en gran medida de conseguir una alta eficiencia de aplicación en el riego. Es muy importante conocer los factores que afectan a la uniformidad de riego, especialmente en aspersores semi-portátiles de gran tamaño, que son un sistema muy común en áreas áridas y semiáridas, como Irán. Hasta el momento, la uniformidad de distribución del agua aplicada no ha sido considerada cuantitativamente en la mayoría de las combinaciones de variables hidráulicas y meteorológicas con aspersores portátiles de gran tamaño. En este trabajo, se ha caracterizado el coeficiente de uniformidad (CU) analizando la influencia de los principales factores que le afectan, como la velocidad del viento (W), la presión de trabajo (P) y el marco de riego. Los ensayos de campo se realizaron con un solo aspersor al aire libre. Se aprecia un efecto significativo del viento, como parámetro meteorológico, sobre el CU bajo diferentes condiciones climáticas, en relación a la presión y la separación entre aspersores. Este comportamiento es muy similar al obtenido con aspersores de tamaño medio. Los criterios técnicos propuestos en los resultados se pueden utilizar para optimizar la gestión del riego por aspersión de acuerdo con factores de diseño adecuados para una amplia gama de condiciones climáticas y presión (es decir 450 y 500 kPa). Así, la relación entre la separación entre aspersores y el radio mojado no debe superar los 0,45 con el fin de alcanzar el coeficiente de diseño de uniformidad aceptable (80%) bajo condiciones de viento (>2 m s -1 ) en el sistema de riego
Hall-effect and resistivity measurements in CdTe and ZnTe at high pressure: Electronic structure of impurities in the zincblende phase and the semi-metallic or metallic character of the high-pressure phases
We carried out high-pressure resistivity and Hall-effect measurements in
single crystals of CdTe and ZnTe up to 12 GPa. Slight changes of transport
parameters in the zincblende phase of CdTe are consitent with the shallow
character of donor impurities. Drastic changes in all the transport parameters
of CdTe were found around 4 GPa, i.e. close to the onset of the cinnabar to
rock-salt transition. In particular, the carrier concentration increases by
more than five orders of magnitude. Additionally, an abrupt decrease of the
resistivity was detected around 10 GPa. These results are discussed in
comparison with optical, thermoelectric, and x-ray diffraction experiments. The
metallic character of the Cmcm phase of CdTe is confirmed and a semi-metallic
character is determined for the rock-salt phase. In zincblende ZnTe, the
increase of the hole concentration by more than two orders of magnitude is
proposed to be due to a deep-to-shallow transformation of the acceptor levels.
Between 9 and 11 GPa, transport parameters are consistent with the
semiconducting character of cinnabar ZnTe. A two orders of magnitude decrease
of the resistivity and a carrier-type inversion occurs at 11 GPa, in agreement
with the onset of the transition to the Cmcm phase of ZnTe. A metallic
character for this phase is deduced.Comment: 20 pages, 4 figure
Geometrical design for pure current-driven domain wall nucleation and shifting
[EN]Nucleation of domain walls by current-driving a single domain wall, confined to the junction area of two symmetrical strips, is investigated using systematic micromagnetic simulations. Secondary domain walls (equivalently, bits encoded in domains) are simultaneously nucleated and driven by alternatively applying current pulses between two terminals in the structure. Simulations show that nanosecond-duration current pulses nucleate and drive series of robust up/down domains even under realistic conditions. These results demonstrate a technique for sequentially nucleating and shifting domain walls without using attached external “bit lines,” fields, or modifying the ferromagnetic strip
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