351 research outputs found
Topological cascade laser for frequency comb generation in -symmetric structures
The cascade of resonant topological structures with -symmetry
breaking is shown to emit laser light with a frequency-comb spectrum. We
consider optically active topological Aubry-Andr\'e-Harper lattices supporting
edge-modes at regularly spaced frequencies. When the amplified resonances in
the -broken regime match the edge modes of the topological
gratings, we predict the emission of discrete laser lines. A proper design
enables to engineer the spectral features for specific applications. The
robustness of the topological protection makes the system very well suited for
a novel generation of compact frequency comb emitters for spectroscopy,
metrology, and quantum information.Comment: 6 pages, 6 figure
Topological lasing and self-induced transparency in two level systems
The use of virtually lossless topologically isolated edge states may lead to
a novel class of thresholdless lasers operating without inversion. One needs
however to understand if topological states may be coupled to external
radiation and act as active cavities. We study a two-level topological
insulator and show that self-induced transparency pulses can directly excite
edge states. We simulate laser emission by a suitable designed topological
cavity, and show that it can emit tunable radiation. For a configuration of
sites following the off-diagonal Aubry-Andre-Harper model we solve the
Maxwell-Bloch equations in the time domain and provide a first principle
confirmation of topological lasers. Our results open the road to a new class of
light emitters with topological protection for applications ranging from
low-cost energetically-effective integrated lasers sources, also including
silicon photonics, to strong coupling devices for studying ultrafast quantum
processes with engineered vacuum
Polariton-polariton scattering in microcavities: A microscopic theory
We apply the fermion commutation technique for composite bosons to
polariton-polariton scattering in semiconductor planar microcavities.
Derivations are presented in a simple and physically transparent fashion. A
procedure of orthogonolization of the initial and final two-exciton state
wavefunctions is used to calculate the effective scattering matrix elements and
the scattering rates. We show how the bosonic stimulation of the scattering
appears in this full fermionic approach whose equivalence to the bosonization
method is thus demonstrated in the regime of low exciton density. We find an
additional contribution to polariton-polariton scattering due to the exciton
oscillator strength saturation, which we analyze as well. We present a theory
of the polariton-polariton scattering with opposite spin orientations and show
that this scattering process takes place mainly via dark excitonic states.
Analytical estimations of the effective scattering amplitudes are given.Comment: Theoretical paper on polariton-polariton scattering in planar
microcavities. The new version contains a slightly modified abstract and a
revised introduction. Typos have been corrected wherever spotted. 16 page
Fundamental collapse of the exciton-exciton effective scattering
The exciton-exciton effective scattering which rules the time evolution of
two excitons is studied as a function of initial momentum difference,
scattering angle and electron-to-hole mass ratio. We show that this effective
scattering can collapse for energy-conserving configurations provided that the
difference between the two initial exciton momenta is larger than a threshold
value. Sizeable scatterings then exist in the forward direction only. We even
find that, for an electron-to-hole mass ratio close to 1/2, the exciton-exciton
effective scattering stays close to zero in all directions when the difference
between the initial exciton momenta has a very specific value. This unexpected
but quite remarkable collapse comes from tricky compensation between direct and
exchange Coulomb processes which originates from the fundamental
undistinguishability of the exciton fermionic components.Comment: Revised text version. Accepted for publication in Physical Review
Alternative polyadenylation of ZEB1 promotes its translation during genotoxic stress in pancreatic cancer cells
Pancreatic ductal adenocarcinoma (PDAC) is characterized by extremely poor prognosis. The standard chemotherapeutic drug, gemcitabine, does not offer significant improvements for PDAC management due to the rapid acquisition of drug resistance by patients. Recent evidence indicates that epithelial-to-mesenchymal transition (EMT) of PDAC cells is strictly associated to early metastasization and resistance to chemotherapy. However, it is not exactly clear how EMT is related to drug resistance or how chemotherapy influences EMT. Herein, we found that ZEB1 is the only EMT-related transcription factor that clearly segregates mesenchymal and epithelial PDAC cell lines. Gemcitabine treatment caused upregulation of ZEB1 protein through post-transcriptional mechanisms in mesenchymal PDAC cells within a context of global inhibition of protein synthesis. The increase in ZEB1 protein correlates with alternative polyadenylation of the transcript, leading to shortening of the 3' untranslated region (UTR) and deletion of binding sites for repressive microRNAs. Polysome profiling indicated that shorter ZEB1 transcripts are specifically retained on the polysomes of PDAC cells during genotoxic stress, while most mRNAs, including longer ZEB1 transcripts, are depleted. Thus, our findings uncover a novel layer of ZEB1 regulation through 3'-end shortening of its transcript and selective association with polysomes under genotoxic stress, strongly suggesting that PDAC cells rely on upregulation of ZEB1 protein expression to withstand hostile environments
Occurrence of gastric cancer and carcinoids in atrophic gastritis during prospective long-term follow up
Objective. Atrophic gastritis (AG) is a risk condition for gastric cancer and type I gastric carcinoids. Recent studies assessing the overall risk of gastric cancer and carcinoids in AG at long-term follow up are lacking. This study aimed to investigate in a prospective cohort of AG patients the occurrence of gastric cancer and carcinoids at long-term follow up. Methods. A total of 200 AG patients from a prospective cohort (67% female, median age 55 years) with a follow up of 7.5 (range: 4-23.4) years were included. Inclusion criteria were presence of AG and at least one follow-up gastroscopy with biopsies at ≥4 years after AG diagnosis. Follow-up gastroscopies at 4-year intervals were performed. Results. Overall, 22 gastric neoplastic lesions were detected (crude incidence 11%). Gastric cancer was diagnosed in four patients at a median follow up of 7.2 years (crude incidence 2%). Eleven type I gastric carcinoids were detected at a median follow up of 5.1 years (crude incidence of 5.5%). In seven patients, six low-grade and one high-grade dysplasia were found. The annual incidence rate person-year were 0.25% (95% confidence interval [CI]: 0.067-0.63%), 0.43% (95% CI: 0.17-0.89%), and 0.68% (95% CI: 0.34-1.21%) for gastric cancer, dysplasia, and type I-gastric carcinoids, respectively. The incidence rates of gastric cancer and carcinoids were not different (p = 0.07). Conclusion. This study shows an annual incidence rate of 1.36% person-year for gastric neoplastic lesions in AG patients at long-term follow up. AG patients are similarly exposed to gastric cancer and type I gastric carcinoids
Melvin J. Hunt v. Albert E. Hunt, Zera A. Hunt, and Douglas J. Hanks : Brief of Appellant
APPEAL OF THE JULY 7, 2004 RULING DENYING PLAINTIFF\u27S REQUEST FOR JUDICIAL DISSOLUTION OF GOLD STREAM CORPORATION; ENTERED IN THE FOURTH DISTRICT COURT, UTAH COUNTY, PROVO DEPARTMENT, THE HONORABLE GARY D. STOTT PRESIDING
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