162 research outputs found
Magnetism and correlations in fractionally filled degenerate shells of graphene quantum dots
When an electron is confined to a triangular atomic thick layer of graphene
[1-5] with zig-zag edges, its energy spectrum collapses to a shell of
degenerate states at the Fermi level (Dirac point) [6-9]. The degeneracy is
proportional to the edge size and can be made macroscopic. This opens up the
possibility to design a strongly correlated electronic system as a function of
fractional filling of the zero-energy shell, in analogy to the fractional
quantum Hall effect in a quasi-two-dimensional electron gas[10], but without
the need for a high magnetic field. In this work we show that electronic
correlations, beyond the Hubbard model[6,7] and mean-field density functional
theory (DFT) [7,8] play a crucial role in determining the nature of the ground
state and the excitation spectrum of triangular graphene quantum dots as a
function of dot size and filling fraction of the shell of zero-energy states.
The interactions are treated by a combination of DFT, tight-binding,
Hartree-Fock and configuration interaction methods (TB-HF-CI) and include all
scattering and exchange terms within second nearest neighbors as well as
interaction with metallic gate. We show that a half filled charge neutral shell
leads to full spin polarization of the island but this magnetic moment is
completely destroyed by the addition of a single electron, in analogy to the
effect of skyrmions on the quantum Hall ferromagnet [11-14] and spin
depolarization in electrostatically defined semiconductor quantum dots[15-18].
The depolarization of the ground state is predicted to result in blocking of
current through a graphene quantum dot due to spin blockade (SB) [18].Comment: v2: minor corrections, new forma
Letter to the editor: The number of urine specimens for bacteriological examination in women
No Abstract. Keywords: asymptomatic bacteriuria, women , urine culture
Radiation properties of an integrated optical leaky wave antenna with periodic silicon perturbations
We propose a highly directive optical leaky wave antenna (OLWA) radiating at 1550 nm composed of a dielectric waveguide comprising periodic silicon (Si) perturbations. The antenna working principle is based on the excitation of a leaky wave guided mode in the perturbed waveguide. Here we study the radiation properties for two sets of perturbation dimensions, and show beam scanning capabilities of the antenna (radiation level and direction) at broadside by varying the free space wavelength. Moreover, the use of Si offers the electronic/optical tunability of its complex refractive index by excess electron-hole carrier density generation via current injection (electronic control) or optical absorption (optical control). Therefore, by changing the Si refractive index we vary the leaky wave attenuation constant and the input impedance of the antenna, which in turn allow for beam control capabilities. © 2012 IEEE
Risk factors of multidrug-resistant bacteria in community-acquired urinary tract infections
Background: Urinary tract infections (UTIs) are one of the most seen
infection among community. Objectives: In this cross-sectional study we
aimed to investigate the risk factors of multidrug-resistant (MDR)
bacteria that caused community-acquired UTI (CA-UTI). Methods:
Consecutive patients admitted to the Urology and Infectious Diseases
policlinics with the diagnosis of CA-UTI were included in the study. A
standard form including possible predisposing factors for MDR bacteria
was applied. Results: In total, 240 patients (51.3% females) were
enrolled in the study. The mean age of participants were 59.8 \ub1
18.3 years old. Escherichia coli (n =166; 69.2%)was the most
frequently isolated bacteria and its incidence was higher in females
than in males (p=0.01). In total, 129 (53.8%) of the identified
pathogens were MDR bacteria. According to multivariate analysis, the
use of antibiotics three or more times increased the risk of infection
with MDR bacteria by 4.6 times, the history of urinary tract infection
in the last 6 months by 2 times, being male and over 65 years old by 3
times. Conclusion: Doctors should consider prescribing broad-spectrum
antibiotics in patients with severe UTIs with a history of UTI,
advanced age, male gender, and multiple antibiotic usage, even if they
have a CA-UTI
Elucidation of key odorants and sensory propertiesof five different extra virgin olive oils from Turkey by GC-MS-Olfactometry
The present study investigates the aroma, key odorants and sensory profile of extra virgin olive oils from five well-known Turkish cultivars. The aromatic extract obtained by the purge and trap extraction system, according to a sensory analysis, resembled the odor of olive oil. A total of 22, 21, 18, 22 and 21 aroma-active compounds were detected in the extracts of Ayvalık, Memecik, Gemlik, Sarı Ulak and Beylik olive oils, respectively. The results show that Ayvalık has the highest flavor dilution (FD) value of 1024 with hexanal, (E)-2-hexenal and α-farnesene. Memecik has the highest FD value at 2048 with (E)-2-hexenal. Gemlik has the highest FD value of 1024 with (Z)-3-hexenyl acetate, (E)-2-hexen-1-ol and α-farnesene. Sarı Ulak has the highest FD value at 2048 with (E)-2-hexenal. Beylik has the highest FD value of 2048 with (E)-2-hexenal and hexanal. All cultivars represent the characteristic green, cut-grass, fruity odor notes
Impact of antimicrobial drug restrictions on doctors' behaviors
Background/aim: Broad-spectrum antibiotics have become available for use only with the approval of infectious disease specialists (IDSs) since 2003 in Turkey. This study aimed to analyze the tendencies of doctors who are not disease specialists (non-IDSs) towards the restriction of antibiotics.Materials and methods: A questionnaire form was prepared, which included a total of 22 questions about the impact of antibiotic restriction (AR) policy, the role of IDSs in the restriction, and the perception of this change in antibiotic consumption. The questionnaire was completed by each participating physician.Results: A total of 1906 specialists from 20 cities in Turkey participated in the study. Of those who participated, 1271 (67.5%) had 5 years of occupational experience in their branch expressed that they followed the antibiotic guidelines more strictly than the JSs (P < 0.05) and 755 of physicians (88%) and 720 of surgeons (84.6%) thought that the AR policy was necessary and useful (P < 0.05).Conclusion: This study indicated that the AR policy was supported by most of the specialists. Physicians supported this restriction policy more so than surgeons did
Phytochemical and nutritional properties of sumac (Rhus coriaria): a potential ingredient for developing functional foods
This is the final version. Available on open access from Elsevier via the DOI in this recordSumac (Rhus coriaria) is a flowering plant that is widely consumed for its promoting health benefits and used in food preparations as a spice in the Mediterranean region. It is a high shrub or small tree with imparipinnate leaves, villus and red fruits with one-seeded drupe, and small greenish-white flowers. The nutraceutical and pharmaceutical potential of sumac makes it a remarkable functional food. In this review, the phytochemical and nutritional properties of sumac as an under valorized functional food have been discussed. Flavonoids, anthocyanins, phenolic acids, and organic acids have been reported as dominant phytochemicals in sumac, which are well known for their pharmacological properties that attract many consumers to commonly choose sumac in their diet as well as food preparations. The remarkable volatile compounds present in sumac give it a unique aroma that increases its acceptance by consumers and potential use in the food industry. Sumac has been evaluated for a broad range of nutritional and pharmacological activities such as antioxidant, antinociceptive, anti-inflammatory, anti-diabetic, hepatoprotective, cardioprotective, anticancer, anti-infertility, and neuroprotective potential. This review has also briefly outlined the safety concerns concerning the use of sumac in terms of toxicology and interactions
Wigner crystal physics in quantum wires
The physics of interacting quantum wires has attracted a lot of attention
recently. When the density of electrons in the wire is very low, the strong
repulsion between electrons leads to the formation of a Wigner crystal. We
review the rich spin and orbital properties of the Wigner crystal, both in the
one-dimensional and quasi-one-dimensional regime. In the one-dimensional Wigner
crystal the electron spins form an antiferromagnetic Heisenberg chain with
exponentially small exchange coupling. In the presence of leads the resulting
inhomogeneity of the electron density causes a violation of spin-charge
separation. As a consequence the spin degrees of freedom affect the conductance
of the wire. Upon increasing the electron density, the Wigner crystal starts
deviating from the strictly one-dimensional geometry, forming a zigzag
structure instead. Spin interactions in this regime are dominated by ring
exchanges, and the phase diagram of the resulting zigzag spin chain has a
number of unpolarized phases as well as regions of complete and partial spin
polarization. Finally we address the orbital properties in the vicinity of the
transition from a one-dimensional to a quasi-one-dimensional state. Due to the
locking between chains in the zigzag Wigner crystal, only one gapless mode
exists. Manifestations of Wigner crystal physics at weak interactions are
explored by studying the fate of the additional gapped low-energy mode as a
function of interaction strength.Comment: 37 pages, 15 figures; v2: references adde
Review of retrospective dosimetry techniques for external ionising radiation exposures
The current focus on networking and mutual assistance in the management of radiation accidents or incidents has demonstrated the importance of a joined-up approach in physical and biological dosimetry. To this end, the European Radiation Dosimetry Working Group 10 on 'Retrospective Dosimetry' has been set up by individuals from a wide range of disciplines across Europe. Here, established and emerging dosimetry methods are reviewed, which can be used immediately and retrospectively following external ionising radiation exposure. Endpoints and assays include dicentrics, translocations, premature chromosome condensation, micronuclei, somatic mutations, gene expression, electron paramagnetic resonance, thermoluminescence, optically stimulated luminescence, neutron activation, haematology, protein biomarkers and analytical dose reconstruction. Individual characteristics of these techniques, their limitations and potential for further development are reviewed, and their usefulness in specific exposure scenarios is discussed. Whilst no single technique fulfils the criteria of an ideal dosemeter, an integrated approach using multiple techniques tailored to the exposure scenario can cover most requirements. © The Author 2010. Published by Oxford University Press. All rights reserved
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