3,693 research outputs found
Preparation and characterization of Bi26–2xMn2xMo10O69-d and Bi26.4Mn0.6Mo10–2yMe2yO69-d(Me = V, Fe) solid solutions
Received: 06.06.2017; accepted: 23.06.2017; published: 14.07.2017.Single phase samples of bismuth molybdate, Bi26Mo10O69, doped with Mn on the bismuth sublattice and V, Fe on the molybdenum sublattice were found to crystallize in the triclinic Bi26Mo10O69 structure at low doping levels and in the monoclinic Bi26Mo10O69 structure - at higher dopant concentration. The assumption that all Mn ions have an oxidation state of +2 was confirmed by means of magnetic measurement results analysis using Curie-Weiss law. Conductivity was investigated using impedance spectroscopy. The conductivity of Bi26.4Mn0.6Mo9.6Fe0.4O69-d was 1.2*10-2 S*cm-1 at 973 K and 2.2*10-4 S*cm-1 at 623 K, and the conductivity of Bi26.4Mn0.6Mo9.2V0.8O69-d was 2.2*10-3 S*cm-1 at 973 K and 2.2*10-5 S*cm-1 at 623 K
Winkle: Foiling Long-Range Attacks in Proof-of-Stake Systems
Winkle protects any validator-based byzantine fault tolerant consensus mechanisms, such as those used in modern Proof-of-Stake blockchains, against long-range attacks where old validators' signature keys get compromised. Winkle is a decentralized secondary layer of client-based validation, where a client includes a single additional field into a transaction that they sign: a hash of the previously sequenced block. The block that gets a threshold of signatures (confirmations) weighted by clients' coins is called a "confirmed"checkpoint. We show that under plausible and flexible security assumptions about clients the confirmed checkpoints can not be equivocated. We discuss how client key rotation increases security, how to accommodate for coins' minting and how delegation allows for faster checkpoints. We evaluate checkpoint latency experimentally using Bitcoin and Ethereum transaction graphs, with and without delegation of stake
Theory of impact interaction between potato bodies and rebounding conveyor
ArticleIn order to increase substantially the quality of the potato heap separation, it is
necessary to carry out the theoretical substantiation of the spiral separator’s parameters with
regard to the impact interaction between the product and the tools of the un
it under the condition
of not damaging the tubers. An equivalent schematic model of the impact interaction between a
potato tuber and the surface of the rebounding conveyor has been devised. Taking into account
the coefficient of restitution of the tuber’s
velocity in case of an impact, new analytical
expressions have been obtained for determining the magnitude and direction of the potato tuber’s
velocity after the impact. They provided the basis for applying the principle of momentum at
impact and obtainin
g the analytical expressions that allow determining the impact impulse and
impact force at the impact of the tuber on the surface of the rebounding conveyor and, eventually,
the dynamic constraints on the permitted velocity of the tuber prior to the impact
interaction under
the condition of not damaging it. A new analytical mathematical model of the impact interaction
of the potato tuber during the potato heap separation has been developed. On the basis of the
obtained theoretical results, studies have been
carried out
on the rational kinematical parameters
of the high
-
quality performance of the above
-
mentioned work process under the condition of
keeping the potato tubers undamaged
Theory of retaining potato bodies during operation of spiral separator
ArticleThe
increase
of the efficiency and quality of
performance of the work process of potato
heap separation can be achieved by means of improving the design of the vibrational spiral
separator and substantiating theoretically its rational parameters under the condition of
eliminating damage to the potato
tubers. An equivalent schematic model of the interaction
between the potato tuber and the surface of the cantilever spiral springs has been devised. On the
basis of the model, the kinematic characteristics of the tuber’s flight and its impact contact with
the elastic surface of the over
mounted rebounding conveyor have been investigated. A new
analytical mathematical model of the potato tuber’s flight from the surface of the spiral
separator
and its subsequent encounter with the
rebounding conveyor mounted above the spiral springs has
been developed. New analytical dependences have been obtained for finding out the distance and
height of the potato tuber’s flight to the point of impact contact as well as the trajectory equation
fo
r the travel to the said contact, which makes it possible to obtain the kinematic constraints
imposed on the allowed rate of travel under
the condition of not damaging the tuber. On the basis
of the obtained analytical dependences, the kinematic parameters
of the improved design of the
spiral potato harvester separator in its interaction with a
potato tuber under
the condition of not
damaging the latter have been investigated
Theory of grain mixture particle motion during aspiration separation
The practice of separating grain mixtures with the use of the difference in the
aerodynamic properties of their components has proved that the process of separating mixtures
in the aspiration separator is the most promising one with regard to the improvement of quality
and intensification of production. The authors have developed a new improved design of
aspiration seed separators, in which the work process of separating seed material is performed
with the use of vibration processes. In this seed material separator, the constant force air flow that
acts on the sail members on the central pipe of the separator, when seeds are fed for processing,
generates self-excited oscillations in the pipe, which produces centrifugal forces of inertia in the
seed feeding system. As a result of the mentioned effect, the propelling force in the process under
study substantially increases, accelerating the seeds of different fractions, which differ in their
masses, to different velocities. The motion paths of the seed particles change accordingly, heavier
particles moving closer to the vertical axis of the aspiration channel, which provides for
increasing the efficiency of separation of the seeds of different fractions from each other. In this
paper, a new mathematical model is developed for the motion of a seed mixture material particle
in the operating space of the separator’s aspiration channel. The mathematical modelling of the
process of vibration and aspiration separation has indicated that the separation of the motion paths
of the medium and heavy fractions takes place within the range of 20–40 mm; the flying speed
of the particles is equal to 3.2–8.0 m s–1, respectively; and their acceleration is equal to 1.8–
3.3 m s–2, which provides the necessary conditions for the accurate and high quality separation
into the required fractions. In view of the found differences between the kinematic characteristics
of the separated fractions of the grain mixture, the diameter of the pipeline for the medium
fraction is to be within the range of 90–100 mm, for the heavy fraction – 50–70 mm
Synthesis, Structure, and Investigation of Bismuth Niobate Doped by Alkaline-Earth Elements
Polycrystalline samples with general formula Bi3
The selection of the amount of anthracene derivatives from raw materials of plant origin and the study of their influence on the rat periodontal
The article presents a new method of ethanol extraction of anthracene derivatives from
the herb St. John's wort, the total content of which was evaluated using a calibration graph.
The drug improved mineral metabolism, showed anti-inflammatory effects in the bone tissue
of the periodontal rats
Overhauser effect in individual InP/GaInP dots
Sizable nuclear spin polarization is pumped in individual InP/GaInP dots in a
wide range of external magnetic fields B_ext=0-5T by circularly polarized
optical excitation. We observe nuclear polarization of up to ~40% at Bext=1.5T
and corresponding to an Overhauser field of ~1.2T. We find a strong feedback of
the nuclear spin on the spin pumping efficiency. This feedback, produced by the
Overhauser field, leads to nuclear spin bi-stability at low magnetic fields of
Bext=0.5-1.5T. We find that the exciton Zeeman energy increases markedly, when
the Overhauser field cancels the external field. This counter-intuitive result
is shown to arise from the opposite contribution of the electron and hole
Zeeman splittings to the total exciton Zeeman energy
- …