13,470 research outputs found
Exotic disordered phases in the quantum model on the honeycomb lattice
We study the ground-state phase diagram of the frustrated quantum
Heisenberg antiferromagnet on the honeycomb lattice using a mean field approach
in terms of the Schwinger boson representation of the spin operators. We
present results for the ground-state energy, local magnetization, energy gap
and spin-spin correlations. The system shows magnetic long range order for
(N\'eel) and (spiral). In the intermediate region, we find two magnetically disordered
phases: a gapped spin liquid phase which shows short-range N\'eel correlations
, and a lattice nematic phase
, which is magnetically disordered
but breaks lattice rotational symmetry. The errors in the values of the phase
boundaries which are implicit in the number of significant figures quoted,
correspond purely to the error in the extrapolation of our finite-size results
to the thermodynamic limit.Comment: 11 pages, 9 figures, to appear in Phys. Rev.
Breaking a quantum key distribution system through a timing side channel
The security of quantum key distribution relies on the validity of quantum
mechanics as a description of nature and on the non-existence of leaky degrees
of freedom in the practical implementations. We experimentally demonstrate how,
in some implementations, timing information revealed during public discussion
between the communicating parties can be used by an eavesdropper to
undetectably access a significant portion of the ``secret'' key.Comment: 6 pages, 4 figures. Added additional references and extended
analysis. Identical to published versio
Dimerized ground states in spin-S frustrated systems
We study a family of frustrated anti-ferromagnetic spin- systems with a
fully dimerized ground state. This state can be exactly obtained without the
need to include any additional three-body interaction in the model. The
simplest members of the family can be used as a building block to generate more
complex geometries like spin tubes with a fully dimerized ground state. After
present some numerical results about the phase diagram of these systems, we
show that the ground state is robust against the inclusion of weak disorder in
the couplings as well as several kinds of perturbations, allowing to study some
other interesting models as a perturbative expansion of the exact one. A
discussion on how to determine the dimerization region in terms of quantum
information estimators is also presented. Finally, we explore the relation of
these results with a the case of the a 4-leg spin tube which recently was
proposed as the model for the description of the compound
CuClDCSO, delimiting the region of the parameter space
where this model presents dimerization in its ground state.Comment: 10 pages, 9 figure
Enzymatic Degumming of Ray Liver Oil Using Phospholipase A1: Efficiency, Yield and Effect on Physicochemical Parameters
Crude oils have components such as metals, pigments, phospholipids and waxes, which alter its physicochemical and organoleptic characteristics. These components are commonly removed during the refining process by physicochemical methods. In recent decades, the oil industry has desired the development of biotechnological processes to replace traditional methods. In this paper the enzymatic degumming of ray liver oil is presented as an alternative innovative, sustainable and process to chemical degumming. The traditional process was performed using citric acid, while the enzymatic process was performed using the enzyme phospholipase A1 as degumming agent. Both treatments were performed in a batch thermostated reactor. The efficiency of the enzyme process, assessed by removing phosphorus percentage content, was significantly higher compared to the traditional treatment, (54.70% and 81.31% respectively). The quality characteristics of crude and degummed oils was determined by acidity, peroxide, p-anisidine and TOTOX indexes, beyond moisture, fatty acids contents, color and density. The fatty acid profile was rich in polyunsaturated omega-3 ratio in all the samples analyzed. Quality parameters evaluated were slightly modified by both degumming processes, highlighting a favorable change in the color and appearance of the oil obtained by the process carried out with enzymes. The obtained results suggest that the enzymatic process produces significant improved quality and nutritional values, with better attempt fish oil characteristics for use in the pharmaceutical and functional foodsFil: Lamas, Daniela Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Massa, Agueda Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentin
Phase diagram study of a dimerized spin-S zig-zag ladder
The phase diagram of a frustrated spin- zig-zag ladder is studied through
different numerical and analytical methods. We show that for arbitrary ,
there is a family of Hamiltonians for which a fully-dimerized state is an exact
ground state, being the Majumdar-Ghosh point a particular member of the family.
We show that the system presents a transition between a dimerized phase to a
N\'eel-like phase for , and spiral phases can appear for large . The
phase diagram is characterized by means of a generalization of the usual Mean
Field Approximation (MFA). The novelty in the present implementation is to
consider the strongest coupled sites as the unit cell. The gap and the
excitation spectrum is analyzed through the Random Phase Approximation (RPA).
Also, a perturbative treatment to obtain the critical points is discussed.
Comparisons of the results with numerical methods like DMRG are also presented.Comment: 14 pages, 6 figures. Some typos were corrected, and notation was
clarifie
- …