843 research outputs found
Spontaneous Pattern Formation in a Polariton Condensate
Polariton condensation can be regarded as a self-organization phenomenon,
where phase ordering is established among particles in the system. In such
condensed systems, further ordering can possibly occur in the particle density
distribution, under particular experimental conditions. In this work we report
on spontaneous pattern formation in a polariton condensate under non-resonant
optical pumping. The slightly elliptical ring-shaped excitation laser we employ
is such to force condensation to occur in a single-energy state with periodic
boundary conditions, giving rise to a multi-lobe standing wave patterned state
Spontaneous self-ordered states of vortex-antivortex pairs in a Polariton Condensate
Polariton condensates have proved to be model systems to investigate
topological defects, as they allow for direct and non-destructive imaging of
the condensate complex order parameter. The fundamental topological excitations
of such systems are quantized vortices. In specific configurations, further
ordering can bring the formation of vortex lattices. In this work we
demonstrate the spontaneous formation of ordered vortical states, consisting in
geometrically self-arranged vortex-antivortex pairs. A mean-field generalized
Gross-Pitaevskii model reproduces and supports the physics of the observed
phenomenology
Relevance of the Heisenberg-Kitaev model for the honeycomb lattice iridates A_2IrO_3
Combining thermodynamic measurements with theoretical density functional and
thermodynamic calculations we demonstrate that the honeycomb lattice iridates
A2IrO3 (A = Na, Li) are magnetically ordered Mott insulators where the
magnetism of the effective spin-orbital S = 1/2 moments can be captured by a
Heisenberg-Kitaev (HK) model with Heisenberg interactions beyond
nearest-neighbor exchange. Experimentally, we observe an increase of the
Curie-Weiss temperature from \theta = -125 K for Na2IrO3 to \theta = -33 K for
Li2IrO3, while the antiferromagnetic ordering temperature remains roughly the
same T_N = 15 K for both materials. Using finite-temperature functional
renormalization group calculations we show that this evolution of \theta, T_N,
the frustration parameter f = \theta/T_N, and the zig-zag magnetic ordering
structure suggested for both materials by density functional theory can be
captured within this extended HK model. Combining our experimental and
theoretical results, we estimate that Na2IrO3 is deep in the magnetically
ordered regime of the HK model (\alpha \approx 0.25), while Li2IrO3 appears to
be close to a spin-liquid regime (0.6 < \alpha < 0.7).Comment: Version accepted for publication in PRL. Additional DFT and
thermodynamic calculations have been included. 6 pages of supplementary
material include
Metastasis of hormone-independent breast cancer to lung and bone is decreased by α-difluoromethylornithine treatment
INTRODUCTION: Polyamines affect proliferation, differentiation, migration and apoptosis of cells, indicating their potential as a target for cancer chemotherapy. Ornithine decarboxylase converts ornithine to putrescine and is the rate-limiting step in polyamine synthesis. α-Difluoromethylornithine (DFMO) irreversibly inhibits ornithine decarboxylase and MDA-MB-435 human breast cancer metastasis to the lung without blocking orthotopic tumor growth. This study tested the effects of DFMO on orthotopic tumor growth and lung colonization of another breast cancer cell line (MDA-MB-231) and the effects on bone metastasis of MDA-MB-435 cells. METHODS: MDA-MB-231 cells were injected into the mammary fat pad of athymic mice. DFMO treatment (2% per orally) began at the day of tumor cell injection or 21 days post injection. Tumor growth was measured weekly. MDA-MB-231 cells were injected into the tail vein of athymic mice. DFMO treatment began 7 days prior to injection, or 7 or 14 days post injection. The number and incidence of lung metastases were determined. Green fluorescent protein-tagged MDA-MB-435 cells were injected into the left cardiac ventricle in order to assess the incidence and extent of metastasis to the femur. DFMO treatment began 7 days prior to injection. RESULTS: DFMO treatment delayed MDA-MB-231 orthotopic tumor growth to a greater extent than growth of MDA-MB-435 tumors. The most substantial effect on lung colonization by MDA-MB-231 cells occurred when DFMO treatment began 7 days before intravenous injection of tumor cells (incidence decreased 28% and number of metastases per lung decreased 35â40%). When DFMO treatment began 7 days post injection, the incidence and number of metastases decreased less than 10%. Surprisingly, treatment initiated 14 days after tumor cell inoculation resulted in a nearly 50% reduction in the number of lung metastases without diminishing the incidence. After intracardiac injection, DFMO treatment decreased the incidence of bone metastases (55% vs 87%) and the area occupied by the tumor (1.66 mm(2 )vs 4.51 mm(2), P < 0.05). CONCLUSION: Taken together, these data demonstrate that DFMO exerts an anti-metastatic effect in more than one hormone-independent breast cancer, for which no standard form of biologically-based treatment exists. Importantly, the data show that DFMO is effective against metastasis to multiple sites and that treatment is generally more effective when administered early
Spin-to-Orbital Angular Momentum Conversion in Semiconductor Microcavities
We experimentally demonstrate a technique for the generation of optical beams
carrying orbital angular momentum using a planar semiconductor microcavity.
Despite being isotropic systems, the transverse electric - transverse magnetic
(TE-TM) polarization splitting featured by semiconductor microcavities allows
for the conversion of the circular polarization of an incoming laser beam into
the orbital angular momentum of the transmitted light field. The process
implies the formation of topological entities, a pair of optical half-vortices,
in the intracavity field
Local magnetism and spin dynamics of the frustrated honeycomb rhodate Li2RhO3
We reportmagnetization, heat capacity, 7Li nuclear magnetic resonance (NMR), and muon-spin rotation (ÎŒSR) measurements on the honeycomb 4d5 spin liquid candidate Li2RhO3. The magnetization in small magnetic fields provides evidence of the partial spin-freezing of a small fraction of Rh4+ moments at 6 K, whereas the Curie-Weiss behavior above 100 K suggests a pseudo-spin-1/2 paramagnet with a moment of about 2.2ÎŒB. The magnetic specific heat (Cm) exhibits no field dependence and demonstrates the absence of long-range magnetic order down to 0.35 K. Cm/T passes through a broad maximum at about 10 K and Cm â T 2 at low temperatures. Measurements of the spin-lattice relaxation rate (1/T1) reveal a gapless slowing-down of spin fluctuations upon cooling with 1/T1 ⌠T 2.2. The results from NMR and ÎŒSR are consistent with a scenario in which a minority of Rh4+ moments are in a short-range correlated frozen state and coexist with a majority of moments in a liquid-like state that continue to fluctuate at low temperatures
Terremoti con effetti macrosismici in Sicilia orientale nel periodo Gennaio 2009 - Dicembre 2013
Sono analizzati ed elaborati i dati dei rilievi macrosismici relativi ai terremoti verificatisi in Sicilia nel periodo
2009-2013. Si tratta di eventi che hanno provocato effetti macrosismici di rilievo e/o danneggiamento per
la maggior parte localizzati nellĂą area etnea, cui si aggiungono alcuni terremoti di magnitudo moderata,
legati a sequenze sismiche significative verificatisi nei settori ibleo, peloritano e eoliano.
I dati sono stati raccolti e elaborati secondo le procedure operative di prassi adottate in questi casi dal gruppo
QUEST (ex-TTC 1.11 Ăą Osservazioni e monitoraggio macrosismico del territorio nazionaleĂą ) dellĂą INGV, e
successivamente parametrizzati secondo gli standard adottati per la compilazione del catalogo CPTI e banca dati
macrosismica DBMI (ex-TTC 5.1 Ăą Banche dati e metodi macrosismiciĂą )
Transcriptional variation of sensory-related genes in natural populations of Aedes albopictus
BACKGROUND: The Asian tiger mosquito, Aedes albopictus, is a highly dangerous invasive vector of numerous medically important arboviruses including dengue, chikungunya and Zika. In four decades it has spread from tropical Southeast Asia to many parts of the world in both tropical and temperate climes. The rapid invasion process of this mosquito is supported by its high ecological and genetic plasticity across different life history traits. Our aim was to investigate whether wild populations, both native and adventive, also display transcriptional genetic variability for functions that may impact their biology, behaviour and ability to transmit arboviruses, such as sensory perception. RESULTS: Antennal transcriptome data were derived from mosquitoes from a native population from Ban Rai, Thailand and from three adventive Mediterranean populations: Athens, Greece and Arco and Trento from Italy. Clear inter-population differential transcriptional activity was observed in different gene categories related to sound perception, olfaction and viral infection. The greatest differences were detected between the native Thai and the Mediterranean populations. The two Italian populations were the most similar. Nearly one million quality filtered SNP loci were identified. CONCLUSION: The ability to express this great inter-population transcriptional variability highlights, at the functional level, the remarkable genetic flexibility of this mosquito species. We can hypothesize that the differential expression of genes, including those involved in sensory perception, in different populations may enable Ae. albopictus to exploit different environments and hosts, thus contributing to its status as a global vector of arboviruses of public health importance. The large number of SNP loci present in these transcripts represents a useful addition to the arsenal of high-resolution molecular markers and a resource that can be used to detect selective pressure and adaptive changes that may have occurred during the colonization process
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