12,921 research outputs found
Raman signatures of classical and quantum phases in coupled dots: A theoretical prediction
We study electron molecules in realistic vertically coupled quantum dots in a
strong magnetic field. Computing the energy spectrum, pair correlation
functions, and dynamical form factor as a function of inter-dot coupling via
diagonalization of the many-body Hamiltonian, we identify structural
transitions between different phases, some of which do not have a classical
counterpart. The calculated Raman cross section shows how such phases can be
experimentally singled out.Comment: 9 pages, 2 postscript figures, 1 colour postscript figure, Latex 2e,
Europhysics Letters style and epsfig macros. Submitted to Europhysics Letter
The SED of Low-Luminosity AGNs at high-spatial resolution
The inner structure of AGNs is expected to change below a certain luminosity
limit. The big blue bump, footprint of the accretion disk, is absent for the
majority of low-luminosity AGNs (LLAGNs). Moreover, recent simulations suggest
that the torus, a keystone in the Unified Model, vanishes for nuclei with L_bol
< 10^42 erg/s. However, the study of LLAGN is a complex task due to the
contribution of the host galaxy, which light swamps these faint nuclei. This is
specially critical in the IR range, at the maximum of the torus emission, due
to the contribution of the old stellar population and/or dust in the nuclear
region. Adaptive optics imaging in the NIR (VLT/NaCo) together with diffraction
limited imaging in the mid-IR (VLT/VISIR) permit us to isolate the nuclear
emission for some of the nearest LLAGNs in the Southern Hemisphere. These data
were extended to the optical/UV range (HST), radio (VLA, VLBI) and X-rays
(Chandra, XMM-Newton, Integral), in order to build a genuine spectral energy
distribution (SED) for each AGN with a consistent spatial resolution (< 0.5")
across the whole spectral range. From the individual SEDs, we construct an
average SED for LLAGNs sampled in all the wavebands mentioned before. Compared
with previous multiwavelength studies of LLAGNs, this work covers the mid-IR
and NIR ranges with high-spatial resolution data. The LLAGNs in the sample
present a large diversity in terms of SED shapes. Some of them are very well
described by a self-absorbed synchrotron (e.g. NGC 1052), while some other
present a thermal-like bump at ~1 micron (NGC 4594). All of them are
significantly different when compared with bright Seyferts and quasars,
suggesting that the inner structure of AGNs (i.e. the torus and the accretion
disk) suffers intrinsic changes at low luminosities.Comment: 8 pages, 5 figures. To appear in the proceedings of "Astrophysics at
High Angular Resolution" (AHAR 2011
Security Evaluation of Support Vector Machines in Adversarial Environments
Support Vector Machines (SVMs) are among the most popular classification
techniques adopted in security applications like malware detection, intrusion
detection, and spam filtering. However, if SVMs are to be incorporated in
real-world security systems, they must be able to cope with attack patterns
that can either mislead the learning algorithm (poisoning), evade detection
(evasion), or gain information about their internal parameters (privacy
breaches). The main contributions of this chapter are twofold. First, we
introduce a formal general framework for the empirical evaluation of the
security of machine-learning systems. Second, according to our framework, we
demonstrate the feasibility of evasion, poisoning and privacy attacks against
SVMs in real-world security problems. For each attack technique, we evaluate
its impact and discuss whether (and how) it can be countered through an
adversary-aware design of SVMs. Our experiments are easily reproducible thanks
to open-source code that we have made available, together with all the employed
datasets, on a public repository.Comment: 47 pages, 9 figures; chapter accepted into book 'Support Vector
Machine Applications
The Role of the Immune Phenotype in Tumor Progression and Prognosis of Patients with Mycosis Fungoides: A Quantitative Immunohistology Whole Slide Approach
Background and objectives: Mycosis fungoides (MF) is the most common type of cutaneous T-cell lymphomas, characterized by mature, skin-tropic CD4+ T-helper cells. In order to study the immune tumor microenvironment in MF patients, we performed immunohistochemical stains on MF biopsies, digitized whole-slide tissue sections, and performed quantitative analysis of the different immune cell subsets to correlate tissue parameters with the clinical data of patients, such as progression-free survival or overall survival. Patients and methods: Overall, 35 patients who were treated between 2009 and 2019 and for whom one or more paraffin tissue blocks were available have been included in the present study (58 tissue specimens in total). Conventional immunohistochemistry stains for CD3, CD4, CD8, CD20 and CD30 were used for the analysis of the immune phenotype, and quantitative analysis was performed using QuPath as a quantitative digital pathology tool for bioimage analysis of whole slides. Results: Analysis of tissue parameters for prognostic significance revealed that patients with a stronger infiltration by CD8+ lymphocytes within the tumor cell compartment had a higher risk of disease progression (p = 0.031) and showed a shorter progress-free survival (p = 0.038). Furthermore, a significant association of the percentage of CD30+ cells (median: 7.8%) with the risk of disease progression (p = 0.023) and progression-free survival (p = 0.023) was found. In relation to the clinical features of our patient cohort, a higher risk of disease progression (p = 0.015) and a shorter progression-free survival (p = 0.032) for older patients (>61 years) were observed. Conclusions: Our results demonstrated the prognostic relevance of large-cell transformation in mycosis fungoides and its strong association with the presence of CD30+ lymphocytes. Unlike previous reports, our study suggests an adverse prognostic role for CD8+ T cells in patients with mycosis fungoides. Moreover, our data indicate that the immune phenotype within the tumor microenvironment shows strong temporal heterogeneity and is altered in the course of tumor progression
Anomalous transport properties of the halfmetallic ferromagnets Co2TiSi, Co2TiGe, and Co2TiSn
In this work the theoretical and experimental investigations of Co2TiZ (Z =
Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is
predicted for all three compounds with only two bands crossing the Fermi energy
in the majority channel. The magnetic moments fulfill the Slater-Pauling rule
and the Curie temperatures are well above room temperature. All compounds show
a metallic like resistivity for low temperatures up to their Curie temperature,
above the resistivity changes to semiconducting like behavior. A large negative
magnetoresistance of 55% is observed for Co2TiSn at room temperature in an
applied magnetic field of 4T which is comparable to the large negative
magnetoresistances of the manganites. The Seebeck coefficients are negative for
all three compounds and reach their maximum values at their respective Curie
temperatures and stay almost constant up to 950 K. The highest value achieved
is -52muV/K m for Co2TiSn which is large for a metal. The combination of
half-metallicity and the constant large Seebeck coefficient over a wide
temperature range makes these compounds interesting materials for
thermoelectric applications and further spincaloric investigations.Comment: 4 pages 4 figure
Bounded derived categories of very simple manifolds
An unrepresentable cohomological functor of finite type of the bounded
derived category of coherent sheaves of a compact complex manifold of dimension
greater than one with no proper closed subvariety is given explicitly in
categorical terms. This is a partial generalization of an impressive result due
to Bondal and Van den Bergh.Comment: 11 pages one important references is added, proof of lemma 2.1 (2)
and many typos are correcte
- …