768 research outputs found
High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots
We compare the quality factor values of the whispery gallery modes of
microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers
by performing room temperature photoluminescence (PL) spectroscopy. The PL
measurements show a large number of high Q factor (Q) resonant modes on the
whole spectrum which allows us to identify the different radial mode families
and to compare them with simulations. We report a considerable improvement of
the Q factor which reflect the etching quality and the relatively low cavity
loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very
high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks
embedding QDs grown on AlGaN barrier layer. We attribute this difference to the
lower absorption below bandgap for AlN barrier layers at the energies of our
experimental investigation
Development and characterization of a human monoclonal antibody for prevention of HCV recurrence in liver transplant patients
More than 170 million people worldwide are chronically infected with hepatitis C virus (HCV) and are at risk of developing liver fibrosis, cirrhosis and hepatocellular carcinoma. Liver transplantation is the only option for patients with HCV-induced end-stage liver diseases. Nevertheless, infection of the newly grafted liver occurs immediately and universally after transplantation. Despite the recent progress in HCV therapy, a prophylactic vaccine is still not available. The role of neutralizing monoclonal antibodies (mAbs) in protection from different viral infections including HCV, HIV and Ebola has been reported. In the last few years, several mAbs with neutralizing activity have been described but only few mAbs have been evaluated in vivo. In the present study, we describe the development of a mAb, designated 2A5, isolated from HCV genotype 1b chronic patient. ELISA results indicated high affinity of mAb 2A5 towards HCV envelope glycoprotein (E1E2). The binding activity was completely lost against denatured E1E2 protein indicating that it targets a conformational epitope within the envelope region. Epitope mapping using alanine mutants of E1E2 proteins defined critical binding residues within the regions 419-447 and 612-617. Results of pseudoparticles (HCVpp) and cell culture produced virus (HCVcc) neutralization showed broad neutralizing activity of mAb 2A5 against all HCV genotypes. The efficacy study of mAb 2A5 in immune-deficient mice of which the liver is repopulated with human hepatocytes (humanized mice) showed complete protection from HCV challenge for genotypes 1a and 4a, while partial protection was achieved for genotypes 1b and 6a. Sequence analysis of E1E2 protein from non-protected mice did not revealed resistance mutations at interaction residues of mAb 2A5. In conclusion, mAb 2A5 shows potent anti-HCV neutralizing activity both in vitro and in vivo and could hence provide an effective strategy to prevent HCV recurrence in chronically infected HCV liver transplant patients. In addition, the broad neutralizing activity of this mAb presents a valuable epitope for the design of HCV vaccine with cross-protection activity
LO-phonon assisted polariton lasing in a ZnO based microcavity
Polariton relaxation mechanisms are analysed experimentally and theoretically
in a ZnO-based polariton laser. A minimum lasing threshold is obtained when the
energy difference between the exciton reservoir and the bottom of the lower
polariton branch is resonant with the LO phonon energy. Tuning off this
resonance increases the threshold, and exciton-exciton scattering processes
become involved in the polariton relaxation. These observations are
qualitatively reproduced by simulations based on the numerical solution of the
semi-classical Boltzmann equations
Patterned silicon substrates: a common platform for room temperature GaN and ZnO polariton lasers
A new platform for fabricating polariton lasers operating at room temperature
is introduced: nitride-based distributed Bragg reflectors epitaxially grown on
patterned silicon substrates. The patterning allows for an enhanced strain
relaxation thereby enabling to stack a large number of crack-free AlN/AlGaN
pairs and achieve cavity quality factors of several thousands with a large
spatial homogeneity. GaN and ZnO active regions are epitaxially grown thereon
and the cavities are completed with top dielectric Bragg reflectors. The two
structures display strong-coupling and polariton lasing at room temperature and
constitute an intermediate step in the way towards integrated polariton
devices
Spectral Phase Control of Interfering Chirped Pulses for High-Energy Narrowband Terahertz Generation
Highly-efficient optical generation of narrowband terahertz (THz) radiation
enables unexplored technologies and sciences from compact electron acceleration
to charge manipulation in solids. State-of-the-art conversion efficiencies are
currently achieved using difference-frequency generation (DFG) driven by
temporal beating of chirped pulses but remain, however, far lower than desired
or predicted. Here we show that high-order spectral phase fundamentally limits
the efficiency of narrowband DFG using chirped-pulse beating and resolve this
limitation by introducing a novel technique based on tuning the relative
spectral phase of the pulses. For optical terahertz generation, we demonstrate
a 13-fold enhancement in conversion efficiency for 1%-bandwidth, 0.361 THz
pulses, yielding a record energy of 0.6 mJ and exceeding previous
optically-generated energies by over an order of magnitude. Our results prove
the feasibility of millijoule-scale applications like terahertz-based electron
accelerators and light sources and solve the long-standing problem of temporal
irregularities in the pulse trains generated by interfering chirped pulses.Comment: 25 pages, 5 figures, updated to the state before review at Nature
Communications (updated the affiliations, title, some content, methods, etc.
Silicon-on-insulator polarization controller with relaxed fabrication tolerances
Polarization control is essential in applications ranging from optical
communications to interferometric sensors. The implementation of in-
tegrated polarization controllers is challenging as they require polariza-
tion rotating waveguides with stringent fabrication tolerances. Here, we
present a fully integrated polarization controller scheme that signi cantly
relaxes the requirements on the rotating waveguides, alleviating fabri-
cation tolerances. We analytically establish a technology-independent,
easily measurable tolerance condition for the rotating waveguides. Po-
larization control in the presence of waveguide width errors of 25% is
shown through full vectorial simulation.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech
Characterization of a gigabit transceiver for the ATLAS inner tracker pixel detector readout upgrade
We present a gigabit transceiver prototype Application Specific Integrated
Circuit (ASIC), GBCR, for the ATLAS Inner Tracker (ITk) Pixel detector readout
upgrade. GBCR is designed in a 65-nm CMOS technology and consists of four
upstream receiver channels, a downstream transmitter channel, and an
Inter-Integrated Circuit (I2C) slave. The upstream channels receive the data at
5.12 Gbps passing through 5-meter 34-American Wire Gauge (AWG) Twin-axial
(Twinax) cables, equalize them, retime them with a recovered clock, and then
drive an optical transmitter. The downstream channel receives the data at 2.56
Gbps from an optical receiver and drives the cable as same as the upstream
channels. The jitter of the upstream channel output is measured to be 35 ps
(peak-peak) when the Clock-Data Recovery (CDR) module is turned on and the
jitter of the downstream channel output after the cable is 138 ps (peak-peak).
The power consumption of each upstream channel is 72 mW when the CDR module is
turned on and the downstream channel consumes 27 mW. GBCR survives the total
ionizing dose of 200 kGy.Comment: 11 pages, 14 figure
Robot companions for citizens
This paper describes the scientific vision and objectives of the FET Flagship candidate initiative Robot Companions for Citizens. Robot Companions will be a new generation of machines that will primarily help and assist elderly people in activities of daily living in their workplace, home and in society. They will be the ICT solution for a new sustainable welfare
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