103 research outputs found
Design of photonic crystal microcavities for cavity QED
We discuss the optimization of optical microcavity designs based on 2D
photonic crystals for the purpose of strong coupling between the cavity field
and a single neutral atom trapped within a hole. We present numerical
predictions for the quality factors and mode volumes of localized defect modes
as a function of geometric parameters, and discuss some experimental challenges
related to the coupling of a defect cavity to gas-phase atoms.Comment: 12 pages, 16 figure
Simulation and Measurement of Pressure Rise in GIS 145 kV due to nternal Arcing
Internal arc testing of metal-enclosed, SF6 gas insulated switchgear (GIS) is defined by IEC 62271-203 and is not a part of mandatory type tests.
However, due to the increasing demands on the safety of personnel, more often the implementation of this test is required in the tender documentation.
According to IEC, the duration of the electric arc is related to the performance of the protective system determined by the first and second
stage of protection. For the rated short-circuit current equal or higher than 40 kA, during the first stage of protection (0.1 s), no external effects on
enclosure other than the operation of pressure relief device is permitted. During the second stage of protection (≤0.3 s) no fragmentation is permitted,
but burn-through is acceptable. The test should be carried out on the GIS compartment with the smallest volume at nominal gas pressure. Since a
newly developed GIS 145 kV is designed as a three-phase encapsulated, arc initiation is achieved by short connecting of all three phase conductors
in the vicinity of a partition by means of a thin metal wire. This ensures that two electric arcs burn simultaneously commutating between the phases,
so the possibility of enclosure burn-through in this type of GIS is minimized. In order to prevent the release of SF6 gas in the atmosphere during the
testing, a test enclosure should be placed in a protective gastight enclosure filled with air or more often SF6 gas at pressure of 0.1 MPa. This test
object configuration significantly complicates the pressure rise calculation and increases the testing cost. In order to prevent enclosure fragmentation,
the pressure difference between the test enclosure and the protective enclosure during the test should always be less than the bursting pressure of
test enclosure. Also, the protective enclosure should be designed to withstand the maximum pressure rise that may occur after pressure relief device
opens. In order to assess the likelihood of passing the upcoming type test for newly developed GIS, a computer program for calculation of pressure
and temperature in the test enclosure and protective enclosure was developed. The mathematical model is based on the paper of the working group
CIGRE A3.24, published in 2014. The basic model shown in the paper is enhanced by the real properties of the SF6 gas/plasma, evaporation of the
electrode material and the insulator ablation. The contribution of exothermic/endothermic reactions between the gas and the electrode material on the
pressure and temperature rise was also considered. At the same time, the measurements of pressure rise in GIS enclosure and protective enclosure
were carried out in Končar High Power Laboratory. The experiments performed on a copper and aluminum electrodes in SF6 gas confirmed significantly
higher contribution of aluminum electrodes to the pressure and temperature rise compared to the copper electrodes. The computer program
is verified by measurement results
Structure of a robust bacterial protein cage and its application as a versatile biocatalytic platform through enzyme encapsulation
Using a newly discovered encapsulin from Mycolicibacterium hassiacum, several biocatalysts were packaged in this robust protein cage. The encapsulin was found to be easy to produce as recombinant protein. Elucidation of its crystal structure revealed that it is a spherical protein cage of 60 protomers (diameter of 23 nm) with narrow pores. By developing an effective coexpression and isolation procedure, the effect of packaging a variety of biocatalysts could be evaluated. It was shown that encapsulation results in a significantly higher stability of the biocatalysts. Most of the targeted cofactor-containing biocatalysts remained active in the encapsulin. Due to the restricted diameters of the encapsulin pores (5–9 Å), the protein cage protects the encapsulated enzymes from bulky compounds. The work shows that encapsulins may be valuable tools to tune the properties of biocatalysts such as stability and substrate specificity
Amniotic Membrane Transplantation for Ocular Surface Reconstruction
The purpose of this study is to analyze the clinical experience and the effect of human
amniotic membrane transplantation on pterygium excision and bullous keratopathy.
From January 1999 to January 2001 at University Hospital »Sestre milosrdnice«
amniotic membrane transplantation was performed consecutively in 21 eyes: 11 eyes
with bullous keratopathy and 10 with recurrent pterygia. In the group with bullous
keratopathy epithelization took place in 19.6 days in 72.7% and the reduction of pain
was satisfactory. Recurrence rate in group with recurrent pterygia was 20%. Based on
the presented results it could be concluded that amniotic membrane transplantation
can be considered as an effective alternative for treating severe ocular surface diseases
and as an alternative for penetrating keratoplasty if there is a lack of graft
Photon-mediated interactions between quantum emitters in a diamond nanocavity
Photon-mediated interactions between quantum systems are essential for realizing quantum networks and scalable quantum information processing. We demonstrate such interactions between pairs of silicon-vacancy (SiV) color centers coupled to a diamond nanophotonic cavity. When the optical transitions of the two color centers are tuned into resonance, the coupling to the common cavity mode results in a coherent interaction between them, leading to spectrally-resolved superradiant and subradiant states. We use the electronic spin degrees of freedom of the SiV centers to control these optically-mediated interactions. Such controlled interactions will be crucial in developing cavity-mediated quantum gates between spin qubits and for realizing scalable quantum network nodes
Liquid-infiltrated photonic crystals - enhanced light-matter interactions for lab-on-a-chip applications
Optical techniques are finding widespread use in analytical chemistry for
chemical and bio-chemical analysis. During the past decade, there has been an
increasing emphasis on miniaturization of chemical analysis systems and
naturally this has stimulated a large effort in integrating microfluidics and
optics in lab-on-a-chip microsystems. This development is partly defining the
emerging field of optofluidics. Scaling analysis and experiments have
demonstrated the advantage of micro-scale devices over their macroscopic
counterparts for a number of chemical applications. However, from an optical
point of view, miniaturized devices suffer dramatically from the reduced
optical path compared to macroscale experiments, e.g. in a cuvette. Obviously,
the reduced optical path complicates the application of optical techniques in
lab-on-a-chip systems. In this paper we theoretically discuss how a strongly
dispersive photonic crystal environment may be used to enhance the light-matter
interactions, thus potentially compensating for the reduced optical path in
lab-on-a-chip systems. Combining electromagnetic perturbation theory with
full-wave electromagnetic simulations we address the prospects for achieving
slow-light enhancement of Beer-Lambert-Bouguer absorption, photonic band-gap
based refractometry, and high-Q cavity sensing.Comment: Invited paper accepted for the "Optofluidics" special issue to appear
in Microfluidics and Nanofluidics (ed. Prof. David Erickson). 11 pages
including 8 figure
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