42 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
Non-abelian Thouless pumping in a photonic lattice
Non-abelian gauge fields emerge naturally in the description of adiabatically
evolving quantum systems having degenerate levels. Here we show that they also
play a role in Thouless pumping in the presence of degenerate bands. To this
end we consider a photonic Lieb lattice having two degenerate non-dispersive
modes and we show that, when the lattice parameters are slowly modulated, the
propagation of the photons bear the fingerprints of the underlying non-abelian
gauge structure. The non-dispersive character of the bands enables a high
degree of control on photon propagation. Our work paves the way to the
generation and detection of non-abelian gauge fields in photonic and optical
lattices.Comment: 11 pages, 6 figure
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
Machine Learning Inverse Problem for Topological Photonics
Topological concepts open many new horizons for photonic devices, from
integrated optics to lasers. The complexity of large scale topological devices
asks for an effective solution of the inverse problem: how best to engineer the
topology for a specific application? We introduce a novel machine learning
approach to the topological inverse problem. We train a neural network system
with the band structure of the Aubry-Andre-Harper model and then adopt the
network for solving the inverse problem. Our application is able to identify
the parameters of a complex topological insulator in order to obtain protected
edge states at target frequencies. One challenging aspect is handling the
multivalued branches of the direct problem and discarding unphysical solutions.
We overcome this problem by adopting a self-consistent method to only select
physically relevant solutions. We demonstrate our technique in a realistic
topological laser design and by resorting to the widely available open-source
TensorFlow library. Our results are general and scalable to thousands of
topological components. This new inverse design technique based on machine
learning potentially extends the applications of topological photonics, for
example, to frequency combs, quantum sources, neuromorphic computing and
metrology
Gastrointestinal stromal tumors: correlation between symptoms at presentation, tumor location and prognostic factors in 47 consecutive patients
<p>Abstract</p> <p>Background</p> <p>Gastrointestinal stromal tumors (GIST) are mesenchymal tumors of the gastrointestinal tract, usually kit-positive, that are believed to originate from interstitial cell of Cajal, or their related stem cells. The most common clinical presentation of these tumors is gastrointestinal bleeding, otherwise they may cause intestinal obstruction, abdominal pain, a palpable mass, or can be incidentally detected during surgery or endoscopic/radiological procedures. Prognosis is related to the size of the tumor and to the mitotic rate; other prognostic factors are tumor location, tumor resection margins, tumor rupture, and c-kit mutation that may interfere with molecular target therapy efficacy.</p> <p>Aim</p> <p>Primary aim of this study was to report our experience regarding GIST patients, correlating symptoms at presentation with tumor localization and risk factors.</p> <p>Patients and methods</p> <p>47 consecutive patients undergone to surgical resection for GISTs were enrolled in a prospective study from December 1999 to March 2009. Patient's clinical and pathological features were collected and analysed.</p> <p>Results</p> <p>The most common symptom was abdominal pain. Bleeding in the digestive tract and abdominal pain were more frequent in gastric GISTs (58% and 61%); acute abdominal symptoms were more frequent in jejunal and ileal GISTs (40% and 60%), p < 0.05. We reported a mild correlation between the mitotic rate index and symptoms at presentation (p 0.074): this correlation was stronger if GISTs causing "acute abdominal symptoms" were compared with GISTs causing "abdominal pain" as main symptom (p 0.039) and with "incidental" GISTs (p 0.022).</p> <p>We observed an higher prevalence of symptomatic patients in the "high risk/malignant group" of both the Fletcher's and Miettines's classification (p < 0.05).</p> <p>Conclusion</p> <p>According with our findings symptoms correlate to tumor location, to class risk criteria as mitotic index and risk classifications, however we cannot conclude that symptoms are <it>per se </it>predictive of survival or patient's outcome.</p
TCD4pos lymphocytosis in rheumatoid and psoriatic arthritis patients following TNFα blocking agents
BACKGROUND:
Lymphocyte expansion and true lymphocytosis are commonly observed in the everyday clinical practice. The meaning of such phenomenon is often poorly understood so that discrimination between benign and malignant lymphocytosis remains difficult to establish. This is mainly true when lymphocytosis rises in patients affected by immune-mediated chronic inflammatory diseases under immunosuppressive treatment, conditions potentially associated with lymphomagenesis. In this brief report the development of mild T CD4pos lymphocytosis in a group of patients with chronic arthritis under anti-TNF-α treatment is described.
METHODS:
Two hundred eight rheumatoid arthritis (RA) and psoriatic arthritis (PsA) patients have been evaluated longitudinally for at least 1-year before and 2-years after anti-TNF-α therapy introduction for the possible appearance of a lymphocyte expansion. In patients who developed lymphocyte expansion, T, B and NK cells were analysed.
RESULTS:
Twenty-five out of 208 (12%) subjects developed a mild T CD4pos lymphocytosis, during anti-TNF-α therapy, which reverted after its interruption. Higher lymphocyte count, more frequent use of steroids and shorter disease duration, before biological therapy start, have emerged as risk factors for lymphocytosis development.
CONCLUSIONS:
This is the first longitudinal cohort study evaluating the onset of lymphocytosis in RA and PsA patients under anti-TNF-α treatment and its possible clinical relevance. A mild T CD4pos lymphocytosis has been observed in 12% of RA and PsA patients probably related to anti-TNF-α treatment as previously reported by anecdotal cases. Patients with higher baseline lymphocyte count, use of steroids and shorter disease duration before the introduction of biologic therapy, seem to be prone to develop this laboratory reversible abnormality
Pattern-tunable synthetic gauge fields in topological photonic graphene
Abstract
We propose a straightforward and effective approach to design, by pattern-tunable strain-engineering, photonic topological insulators supporting high quality factors edge states. Chiral strain-engineering creates opposite synthetic gauge fields in two domains resulting in Landau levels with the same energy spacing but different topological numbers. The boundary of the two topological domains hosts robust time-reversal and spin-momentum-locked edge states, exhibiting high quality factors due to continuous strain modulation. By shaping the synthetic gauge field, we obtain remarkable field confinement and tunability, with the strain strongly affecting the degree of localization of the edge states. Notably, the two-domain design stabilizes the strain-induced topological edge state. The large potential bandwidth of the strain-engineering and the opportunity to induce the mechanical stress at the fabrication stage enables large scalability for many potential applications in photonics, such as tunable microcavities, new lasers, and information processing devices, including the quantum regime
Direct Observation of Topological Protected Edge States in Slow-Light
We use split-ring resonators to demonstrate topologically protected edge
states in the Su-Schieffer-Heeger model experimentally, but in a slow-light
wave with the group velocity down to of light speed in free space. A
meta-material formed by an array of complementary split-ring resonators with
controllable hopping strength enables the direct observation in transmission
and reflection of non-trivial topology eigenstates, including a negative phase
velocity regime. By rotating the texture orientation of the diatomic
resonators, we can explore all the band structures and unveil the onset of the
trivial and non-trivial protected eigenmodes at GHz frequencies, even in the
presence of non-negligible loss. Our system realizes a fully tunable and
controllable artificial optical system to study the interplay between topology
and slow-light towards applications in quantum technologies.Comment: 5 pages, 4 figure
Autoantibodies toward ATP4A and ATP4B subunits of gastric proton pump H+,K+-ATPase are reliable serological pre-endoscopic markers of corpus atrophic gastritis
INTRODUCTION: Noninvasive assessment of corpus atrophic gastritis (CAG), a condition at increased risk of gastric cancer, is based on the measurement of pepsinogens, gastrin, and Helicobacter pylori antibodies. Parietal cell autoantibodies (PCAs) against the gastric proton pump (ATP4) are potential serological biomarkers of CAG. The purpose of this study was to compare the diagnostic performance of PCA and pepsinogen I tests in patients with clinical suspicion of CAG with the histopathological evaluation of gastric biopsies as reference standard.
METHODS: A prospective case-finding study was performed on 218 naive adult patients (131 women, median age 65 years) who underwent gastric biopsies to confirm/exclude CAG. Patients with histopathological CAG were defined as cases, conversely as controls. Autoantibodies against the individual alpha (ATP4A) and beta (ATP4B) subunits of ATP4 were measured by luciferase immunoprecipitation, and global PCA and pepsinogen I by enzyme-linked immunosorbent assay.
RESULTS: Histopathology classified 107 subjects (49%) as cases (CAG+, autoimmune 81.2%, and multifocal extensive 18.8%) and 111 subjects (51%) as controls (CAG−). In cases, ATP4A, ATP4B, and PCA titers were increased compared with controls, whereas pepsinogen I was reduced (P < 0.0001 for all). ATP4B, ATP4A, and pepsinogen I tests showed sensitivities of 77%, 75%, and 73% and specificities of 88%, 88%, and 80%, respectively. The receiver operating characteristic (ROC) area under the ROC curve (AUC) of these serological biomarkers confirmed their ability to discriminate cases from controls (ATP4B = 0.838, ATP4A = 0.826, pepsinogen I = 0.775, and PCA = 0.805), whereas the partial ROC-pAUC90 analysis showed that the ATP4B test had the best diagnostic performance (P = 0.008 vs ATP4; P = 0.0002 vs pepsinogen I). The presence of autoimmune or extensive gastritis was not significantly different between ATP4B positive or negative cases (P = 0.217).
DISCUSSION: PCAs are promising serological biomarkers for the identification of CAG in high-risk individuals, particularly in an autoimmune pattern but also in an extensive-multifocal atrophy pattern