9,641 research outputs found
PDFS: Practical Data Feed Service for Smart Contracts
Smart contracts are a new paradigm that emerged with the rise of the
blockchain technology. They allow untrusting parties to arrange agreements.
These agreements are encoded as a programming language code and deployed on a
blockchain platform, where all participants execute them and maintain their
state. Smart contracts are promising since they are automated and
decentralized, thus limiting the involvement of third trusted parties, and can
contain monetary transfers. Due to these features, many people believe that
smart contracts will revolutionize the way we think of distributed
applications, information sharing, financial services, and infrastructures.
To release the potential of smart contracts, it is necessary to connect the
contracts with the outside world, such that they can understand and use
information from other infrastructures. For instance, smart contracts would
greatly benefit when they have access to web content. However, there are many
challenges associated with realizing such a system, and despite the existence
of many proposals, no solution is secure, provides easily-parsable data,
introduces small overheads, and is easy to deploy.
In this paper we propose PDFS, a practical system for data feeds that
combines the advantages of the previous schemes and introduces new
functionalities. PDFS extends content providers by including new features for
data transparency and consistency validations. This combination provides
multiple benefits like content which is easy to parse and efficient
authenticity verification without breaking natural trust chains. PDFS keeps
content providers auditable, mitigates their malicious activities (like data
modification or censorship), and allows them to create a new business model. We
show how PDFS is integrated with existing web services, report on a PDFS
implementation and present results from conducted case studies and experiments.Comment: Blockchain; Smart Contracts; Data Authentication; Ethereu
Magnetic Fourier Integral Operators
In some previous papers we have defined and studied a 'magnetic'
pseudodifferential calculus as a gauge covariant generalization of the Weyl
calculus when a magnetic field is present. In this paper we extend the standard
Fourier Integral Operators Theory to the case with a magnetic field, proving
composition theorems, continuity theorems in 'magnetic' Sobolev spaces and
Egorov type theorems. The main application is the representation of the
evolution group generated by a 1-st order 'magnetic' pseudodifferential
operator (in particular the relativistic Schr\"{o}dinger operator with magnetic
field) as such a 'magnetic' Fourier Integral Operator. As a consequence of this
representation we obtain some estimations for the distribution kernel of this
evolution group and a result on the propagation of singularities
Ab initio theory of helix-coil phase transition
In this paper we suggest a theoretical method based on the statistical
mechanics for treating the alpha-helix-random coil transition in alanine
polypeptides. We consider this process as a first-order phase transition and
develop a theory which is free of model parameters and is based solely on
fundamental physical principles. It describes essential thermodynamical
properties of the system such as heat capacity, the phase transition
temperature and others from the analysis of the polypeptide potential energy
surface calculated as a function of two dihedral angles, responsible for the
polypeptide twisting. The suggested theory is general and with some
modification can be applied for the description of phase transitions in other
complex molecular systems (e.g. proteins, DNA, nanotubes, atomic clusters,
fullerenes).Comment: 24 pages, 3 figure
New selection rules for resonant Raman scattering on quantum wires
The bosonisation technique is used to calculate the resonant Raman spectrum
of a quantum wire with two electronic sub-bands occupied. Close to resonance,
the cross section at frequencies in the region of the inter sub-band
transitions shows distinct peaks in parallel polarisation of the incident and
scattered light that are signature of collective higher order spin density
excitations. This is in striking contrast to the conventional selection rule
for non-resonant Raman scattering according to which spin modes can appear only
in perpendicular polarisation. We predict a new selection rule for the
excitations observed near resonance, namely that, apart from charge density
excitations, only spin modes with positive group velocities can appear as peaks
in the spectra in parallel configuration close to resonance. The results are
consistent with all of the presently available experimental data.Comment: 7 pages, 2 figure
Effect of Ethylenediaminetetraacetic Acid and Ammonium Oxalate on the Prevalence of Microorganisms and Removal of Aluminum in Soil by Bitter Leaf Plant (Vernonia amygdalina Delile)
This research was carried out to investigate effect of ethylenediaminetetraacetic acid and ammonium oxalate on the prevalence of microorganisms and removal of aluminum in soil by bitter leaf plant (Vernonia amygdalina). The test plant was sown in aluminium-polluted soil (conc. = 150mg Al kg-1 soil). One gram of each chelating agent was dissolved in 1.5 litres of water and applied at different time intervals; application on a day prior to sowing of test plant in metal-polluted soil, application on the day of planting, application at one week after planting; at one month after planting. For the control soils, chelating agent were not added, although aluminium-contaminated. In the control, aluminium concentrations in leaf tissues were 16.20mg/kg compared to a staggering 9.20mg/kg in EW1 and 5.24mg/kg in OD1. However, heavy metal concentration of the leaves of Vernonia amygdalina in the control, EW1, EM1, OD-1 and OW1 were significantly similar (P>0.05). Concentration of aluminium in the stem tissues were also similar in ED1, EM1, OD-1, OD1 and OW1 (P>0.05) were concentration ranged from 5.42mg/kg to 7.98mg/kg. Compared to the control, aluminium concentration in stem tissues was 4.95mg/kg comparable with 3.42mg/kg in OM1. In the plant root, OD1 had the highest accumulation of aluminium in the root (16.92mg/kg); however concentrations of aluminium in the roots were also statically similar in OW1 (15.08mg/kg), OM1 (13.84mg/kg), OD-1 (14.72mg/kg), EM1 (15.12mg/kg) and in the control (13.52mg/kg). Results of the following also showed concentrations of residual aluminium in the soil ranging from 68.25mg/kg in the control to 109.85mg/kg in ED1 soil. After three months of planting, results show that the total bacteria count for ED1 (5.3 × 104 cfu/g) had the highest while OM1 (3.9 × 103 cfu/g) had the lowest. For fungi isolates, the highest was control (8.2 × 103 cfu/g) whereas the lowest were OD–1 (6.8 × 102 cfu/g). The most prevalent microorganisms in the spiked soil with heavy metal are Bacillus subtilis represented in all the samples for bacteria while Aspergillus niger representing fungi. The perseverance of the test plant in the aluminium spiked soil is an indication of adaptation to the stress imposed by the concentration of aluminium in soil. In spite of the metal composition within the soil, it was observed that a number of microorganisms existed. This may therefore suggest a favourable environment for the microorganisms within the soil rhizospheric region of Vernonia amygdalina.Keywords: EDTA, oxalate, aluminium, pollution, remediation, Vernonia amygdalin
Delineation of the Native Basin in Continuum Models of Proteins
We propose two approaches for determining the native basins in off-lattice
models of proteins. The first of them is based on exploring the saddle points
on selected trajectories emerging from the native state. In the second
approach, the basin size can be determined by monitoring random distortions in
the shape of the protein around the native state. Both techniques yield the
similar results. As a byproduct, a simple method to determine the folding
temperature is obtained.Comment: REVTeX, 6 pages, 5 EPS figure
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