10,909 research outputs found
Method and device for the detection of phenol and related compounds
A method is described which permits the selective oxidation and potentiometric detection of phenol and related compounds in an electrochemical cell. An anode coated with a gel immobilized oxidative enzyme and a cathode are each placed in an electrolyte solution. The potential of the cell is measured by a potentiometer connected to the electrodes
New method for calculating helicity amplitudes of jet-like QED processes for high-energy colliders II. Processes with lepton pair production
As continuation of our previous paper we further develop our new method for
calculating helicity amplitudes of jet-like QED processes described by tree
diagrams, applying it to lepton pair production. This method consists in
replacing spinor structures for real and weakly virtual intermediate leptons by
simple transition vertices. New vertices are introduced for the pair production
case, and previous bremsstrahlung vertices are generalized to include virtual
photons inside the considered jet. We present a diagrammatic approach that
allows to write down in an efficient way the leading helicity amplitudes, at
tree level. The obtained compact amplitudes are particularly suitable for
numerical calculations in jet-like kinematics. Several examples with up to four
particles in a jet are discussed in detail.Comment: 11 pages, 11 figures, Latex, Springer-Latex macros include
New method for calculating helicity amplitudes of jet--like QED processes for high--energy colliders I. Bremsstrahlung processes
Inelastic QED processes, the cross sections of which do not drop with
increasing energy, play an important role at high-energy colliders. Such
reactions have the form of two-jet processes with the exchange of a virtual
photon in the t-channel. We consider them in the region of small scattering
angles , which yields the dominant contribution to
their total cross sections. A new effective method is presented and applied to
QED processes with emission of real photons to calculate the helicity
amplitudes of these processes. Its basic idea is similar to the well-known
equivalent-lepton method. Compact analytical expressions for those amplitudes
up to are derived omitting only terms of the order of , and higher order. The helicity amplitudes are presented
in a compact form in which large compensating terms are already cancelled. Some
common properties for all jet-like processes are found and we discuss their
origin.Comment: 17 pages, LATEX (svjour style files included
Matter near to the Endpoint of the Electroweak Phase Transition
Wave functions and the screening mass spectrum in the 3D SU(2)-Higgs model
near to the phase transition line below the endpoint and in the crossover
region are calculated. In the crossover region the changing spectrum versus
temperature is examined showing the aftermath of the phase transition at lower
Higgs mass. Large sets of operators with various extensions are used allowing
to identify wave functions in position space.Comment: 3 pages, 8 figures, LaTex+espcrc2.sty; LATTICE98(electroweak
Quantum phase transitions, frustration, and the Fermi surface in the Kondo lattice model
The quantum phase transition from a spin-Peierls phase with a small Fermi
surface to a paramagnetic Luttinger-liquid phase with a large Fermi surface is
studied in the framework of a one-dimensional Kondo-Heisenberg model that
consists of an electron gas away from half filling, coupled to a spin-1/2 chain
by Kondo interactions. The Kondo spins are further coupled to each other with
isotropic nearest-neighbor and next-nearest-neighbor antiferromagnetic
Heisenberg interactions which are tuned to the Majumdar-Ghosh point. Focusing
on three-eighths filling and using the density-matrix renormalization-group
(DMRG) method, we show that the zero-temperature transition between the phases
with small and large Fermi momenta appears continuous, and involves a new
intermediate phase where the Fermi surface is not well defined. The
intermediate phase is spin gapped and has Kondo-spin correlations that show
incommensurate modulations. Our results appear incompatible with the local
picture for the quantum phase transition in heavy fermion compounds, which
predicts an abrupt change in the size of the Fermi momentum.Comment: 9 pages, 8 figure
Translational cooling and storage of protonated proteins in an ion trap at subkelvin temperatures
Gas-phase multiply charged proteins have been sympathetically cooled to
translational temperatures below 1 K by Coulomb interaction with laser-cooled
barium ions in a linear ion trap. In one case, an ensemble of 53 cytochrome c
molecules (mass ~ 12390 amu, charge +17 e) was cooled by ~ 160 laser-cooled
barium ions to less than 0.75 K. Storage times of more than 20 minutes have
been observed and could easily be extended to more than an hour. The technique
is applicable to a wide variety of complex molecules.Comment: same version as published in Phys. Rev.
The Role of the Internet of Things in Network Resilience
Disasters lead to devastating structural damage not only to buildings and
transport infrastructure, but also to other critical infrastructure, such as
the power grid and communication backbones. Following such an event, the
availability of minimal communication services is however crucial to allow
efficient and coordinated disaster response, to enable timely public
information, or to provide individuals in need with a default mechanism to post
emergency messages. The Internet of Things consists in the massive deployment
of heterogeneous devices, most of which battery-powered, and interconnected via
wireless network interfaces. Typical IoT communication architectures enables
such IoT devices to not only connect to the communication backbone (i.e. the
Internet) using an infrastructure-based wireless network paradigm, but also to
communicate with one another autonomously, without the help of any
infrastructure, using a spontaneous wireless network paradigm. In this paper,
we argue that the vast deployment of IoT-enabled devices could bring benefits
in terms of data network resilience in face of disaster. Leveraging their
spontaneous wireless networking capabilities, IoT devices could enable minimal
communication services (e.g. emergency micro-message delivery) while the
conventional communication infrastructure is out of service. We identify the
main challenges that must be addressed in order to realize this potential in
practice. These challenges concern various technical aspects, including
physical connectivity requirements, network protocol stack enhancements, data
traffic prioritization schemes, as well as social and political aspects
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