364 research outputs found
Variational Approach for the Effects of Periodic Modulations on the Spectrum of Massless Dirac Fermion
In the variational framework, we study the electronic energy spectrum of
massless Dirac fermions of graphene subjected to one-dimensional oscillating
magnetic and electrostatic fields centered around a constant uniform static
magnetic field. We analyze the influence of the lateral periodic modulations in
one direction, created by these oscillating electric and magnetic fields, on
Dirac like Landau levels depending on amplitudes and periods of the field
modulations. We compare our theoretical results with those found within the
framework of non-degenerate perturbation theory. We found that the technique
presented here yields energies lower than that obtained by the perturbation
calculation, and thus gives more stable solutions for the electronic spectrum
of massless Dirac fermion subjected to a magnetic field perpendicular to
graphene layer under the influence of additional periodic potentials.Comment: 8 pages, 7 figure
Boundaries of Subcritical Coulomb Impurity Region in Gapped Graphene
The electronic energy spectrum of graphene electron subjected to a
homogeneous magnetic field in the presence of a charged Coulomb impurity is
studied analytically within two-dimensional Dirac-Weyl picture by using
variational approach. The variational scheme we used is just based on utilizing
the exact eigenstates of two-dimensional Dirac fermion in the presence of a
uniform magnetic field as a basis for determining analytical energy eigenvalues
in the presence of an attractive/repulsive charged Coulomb impurity. This
approach allows us to determine under which conditions bound state solutions
can or can not exist in gapped graphene in the presence of magnetic field. In
addition, the effects of uniform magnetic field on the boundaries of
subcritical Coulomb impurity region in the massless limit are also analyzed.
Our analytical results show that the critical impurity strength decreases with
increasing gap/mass parameter, and also that it increases with increasing
magnetic field strength. In the massless limit, we investigate that the
critical Coulomb coupling strength is independent of magnetic field, and its
upper value for the ground-state energy is 0.752.Comment: 9 pages,10 figure
Effect of heparin in the intraocular irrigating solution on postoperative inflammation in the pediatric cataract surgery
Yelda B Özkurt, Arzu Taskiran, Nadire Erdogan, Baran Kandemir, Ömer K Dog?anDepartment of Ophthalmology, Kartal Training and Research Hospital, Istanbul, TurkeyPurpose: To evaluate the influence of irrigation of the anterior chamber with heparin sodium on postoperative inflammation after pediatric cataract surgery. Setting: Kartal Training and Research Hospital, First Eye Clinic, Istanbul, Turkey.Design: Randomized prospective double-blind study.Methods: Fourteen consecutive eyes from 14 patients aged 8.9 ± 5.9 years, (range 3–18 years) (group 1) and 19 eyes from 19 patients aged 9.1 ± 5.2 (range 1.5–18 years) (group 2) underwent pediatric cataract surgery. Five patients in group 1 were between three and five years old. One patient was 1.5 years old and six patients in group 2 were between three and five years old. During the procedure, group 1 received anterior chamber irrigation with heparin sodium (5 IU/cc) and 1 ml of heparin sodium (concentration 10 IU/ml) added to the irrigating balanced salt solution (BSS Plus; Alcon Laboratories, Inc., Fort Worth, TX, USA) while group 2 received BSS without heparin sodium only. Cases aged under three years received anterior vitrectomy in addition to posterior capsulorrhexis. One eye received anterior vitrectomy in group 1 and two eyes received anterior vitrectomy in group 2. Cases with preoperative complications were not included in the study. Early and late postoperative inflammatory complications, including fibrin formation, anterior and posterior synechia, cyclitic and pupillary membrane formation were recorded and compared.Results: Mild anterior chamber reaction was observed in three patients in Group 1, while nine cases in group 2 experienced marked anterior chamber reaction. In four of nine patients from group 2, anterior chamber reaction was severe and resulted in pupillary membrane and synechia despite treatment in the postoperative 7th day, while in all three cases in group 1, reaction disappeared by the 7th day.Conclusion: Anterior chamber irrigation with heparin during pediatric cataract surgery may minimize early inflammatory reaction and decrease the number of postoperative inflammatory related complications.Keywords: pediatric, cataract, surgery, inflammatio
Two Electrons in a Quantum Dot: A Unified Approach
Low-lying energy levels of two interacting electrons confined in a
two-dimensional parabolic quantum dot in the presence of an external magnetic
field have been revised within the frame of a novel model. The present
formalism, which gives closed algebraic solutions for the specific values of
magnetic field and spatial confinement length, enables us to see explicitly
individual effects of the electron correlation.Comment: 14 page
Quantification of rotator cuff tear geometry: the repair ratio as a guide for surgical repair in crescent and U-shaped tears
Surgical repair of symptomatic, retracted rotator cuff tears unresponsive to non-operative treatments requires closure of the tear without undue tension and reattaching the torn tendon to its former insertion site. In this study, the length of the torn tendon edge was hypothesized to be longer than the length of the humeral insertion site. The objective of this study was to quantify the discrepancy in length of the torn tendon edge and the length of the avulsed humeral insertion site.
Full thickness, rotator cuff tears that were found in twelve fresh frozen cadaver shoulders was studied. The length of the torn tendon edge, the length of the avulsed humeral insertion site and the retraction were measured using digital calipers.
Each tear involved the supraspinatus and the infraspinatus was additionally torn in six. The size of the tear was medium in eight and large in four. The length of the torn tendon edge was always longer than the length of the avulsed humeral insertion site. Retraction was 29.9 ± 9.3 mm (range 21–48 mm). The repair ratio, defined as the ratio of length of torn tendon edge to the length of avulsed humeral insertion site, was 2.6 ± 0.4 (range 2.1–3.5).
As only the length of the torn tendon edge equal to the length of the avulsed humeral insertion site can be repaired to bone, a repair ratio more than one precludes a simple repair and an additional repair technique such as margin convergence would be necessary for the remaining unapproximated torn tendon edge in rotator cuff tears. Repair ratio may aid in selection of the surgical repair technique of these rotator cuff tears
Can taraxacum officinale (dandelion) extract be an alternative of paracetamol in inflammatory and painful cases? an evaluation with regard to biochemical and reproductive parameters
The aim of this study was to investigate the usage of Taraxacum officinale extract (TOE) in inflammatory and painful cases as an alternative to paracetamol (PRC)
through the assessment of biochemical and reproductive parameters. Totally, 30 male Sprague Dawley rats aged eight weeks old, were used in this study. The
animals were obtained from Atatürk University Experimental Research and Application Centre and kept under standard laboratory conditions. Commercial
pellet chow and fresh drinking water were available ad libitum. Rats were divided into five groups: Group I (n= 6); referred as control. Group II (n=6); referred as
TOE150 (150 mg/kg). Group III (n=6); referred as TOE200 (200 mg/kg). Group IV (n=6); referred as TOE250 (250 mg/kg). Group V (n=6); referred as Paracetamol
(PRC) (2 g/kg). The treatment was performed for consecutive 8 days. The animals were tranquilized and sacrificed on 9th day of study. Blood samples, cauda
epididymal semen samples and testes tissues were collected. Routine semen examinations were performed and oxidative stress levels of testicular tissues
were assayed. Reproductive organ weights [total testes weight (TTW) and total cauda epididymal weights (TCEW)] were recorded. Motility in TOE250 group
was significantly higher when compared to the other groups (P<0.05). Velocity of sperm cells in PRC group was significantly lower when compared to the
other groups (P<0.05). Dead sperm rate in control group was significantly higher when compared to the other groups (P<0.001). On the other hand, the lowest
TCEW was in TOE150 group (P<0.05). There were no differences in terms of TTW among all groups. Malondialdehyde (MDA) level of PRC group was significantly
higher than the treatment groups (P<0.05). Besides, glutathione peroxidase (GPx) levels of PRC group were lower than the other groups (P<0.001). Superoxide
dismutase (SOD) level of PRC group was significantly lower than the treatment groups (P<0.001). The lowest catalase (CAT) level was in PRC group and the
highest glutathione (GSH) level was in T200 group (P<0.001). In conclusion, it was observed that TOE could use as alternative of PRC and hence can be avoided
from negative effects of PRC on biochemical and reproductive parameters
Does shear wave ultrasound independently predict axillary lymph node metastasis in women with invasive breast cancer?
Shear wave elastography (SWE) shows promise as an adjunct to greyscale ultrasound examination in assessing breast masses. In breast cancer, higher lesion stiffness on SWE has been shown to be associated with features of poor prognosis. The purpose of this study was to assess whether lesion stiffness at SWE is an independent predictor of lymph node involvement. Patients with invasive breast cancer treated by primary surgery, who had undergone SWE examination were eligible. Data were retrospectively analysed from 396 consecutive patients. The mean stiffness values were obtained using the Aixplorer(®) ultrasound machine from SuperSonic Imagine Ltd. Measurements were taken from a region of interest positioned over the stiffest part of the abnormality. The average of the mean stiffness value obtained from each of two orthogonal image planes was used for analysis. Associations between lymph node involvement and mean lesion stiffness, invasive cancer size, histologic grade, tumour type, ER expression, HER-2 status and vascular invasion were assessed using univariate and multivariate logistic regression. At univariate analysis, invasive size, histologic grade, HER-2 status, vascular invasion, tumour type and mean stiffness were significantly associated with nodal involvement. Nodal involvement rates ranged from 7 % for tumours with mean stiffness <50 kPa to 41 % for tumours with a mean stiffness of >150 kPa. At multivariate analysis, invasive size, tumour type, vascular invasion, and mean stiffness maintained independent significance. Mean stiffness at SWE is an independent predictor of lymph node metastasis and thus can confer prognostic information additional to that provided by conventional preoperative tumour assessment and staging
- …