1,995 research outputs found
Similarity solutions and Conservation laws for the Bogoyavlensky-Konopelchenko Equation by Lie point symmetries
The 1 + 2 dimensional Bogoyavlensky-Konopelchenko Equation is investigated
for its solution and conservation laws using the Lie point symmetry analysis.
In the recent past, certain work has been done describing the Lie point
symmetries for the equation and this work seems to be incomplete (Ray S (2017)
Compt. Math. Appl. 74, 1157). We obtained certain new symmetries and
corresponding conservation laws. The travelling-wave solution and some other
similarity solutions are studied.Comment: 12 pages. Accepted for publication in Quaestiones Mathematica
Noether's Theorem and Symmetry
In Noether's original presentation of her celebrated theorm of 1918 allowance
was made for the dependence of the coefficient functions of the differential
operator which generated the infinitesimal transformation of the Action
Integral upon the derivatives of the depenent variable(s), the so-called
generalised, or dynamical, symmetries. A similar allowance is to be found in
the variables of the boundary function, often termed a gauge function by those
who have not read the original paper. This generality was lost after texts such
as those of Courant and Hilbert or Lovelock and Rund confined attention to
point transformations only. In recent decades this dimunition of the power of
Noether's Theorem has been partly countered, in particular in the review of
Sarlet and Cantrijn. In this special issue we emphasise the generality of
Noether's Theorem in its original form and explore the applicability of even
more general coefficient functions by alowing for nonlocal terms. We also look
for the application of these more general symmetries to problems in which
parameters or parametric functions have a more general dependence upon the
independent variablesComment: 23 pages, to appear in Symmetry in the special issue "Noether's
Theorem and Symmetry", dedicated for the 100 years from the publication of E.
Noether's original work on the invariance of the functional of the Calculus
of Variation
Detector imperfections in photon-pair source characterization
We analyze how imperfections in single-photon detectors impact the
characterization of photon-pair sources. We perform exact calculations to
reveal the effects of multi-pair emissions and of noisy, non-unit efficiency,
non photon-number resolving detections on the Cauchy-Schwarz parameter, on the
second order auto-correlation and cross-correlation functions, and on the
visibilities of both Hong-Ou-Mandel and Bell-like interferences. We consider
sources producing either two-mode squeezed states or states with a Poissonian
photon distribution. The proposed formulas are useful in practice to determine
the impacts of multi-pair emissions and dark counts in standard tests used in
quantum optics.Comment: 9 pages, 11 figure
Reciprocal space mapping of magnetic order in thick epitaxial MnSi films
We report grazing incidence small angle neutron scattering (GISANS) and
complementary off-specular neutron reflectometry (OSR) of the magnetic order in
a single-crystalline epitaxial MnSi film on Si(111) in the thick film limit.
Providing a means of direct reciprocal space mapping, GISANS and OSR reveal a
magnetic modulation perpendicular to the films under magnetic fields parallel
and perpendicular to the film, where additional polarized neutron reflectometry
(PNR) and magnetization measurements are in excellent agreement with the
literature. Regardless of field orientation, our data does not suggest the
presence of more complex spin textures, notably the formation of skyrmions.
This observation establishes a distinct difference with bulk samples of MnSi of
similar thickness under perpendicular field, in which a skyrmion lattice
dominates the phase diagram. Extended x-ray absorption fine structure
measurements suggest that small shifts of the Si positions within the
unstrained unit cell control the magnetic state, representing the main
difference between the films and thin bulk samples
Crossover from antiferromagnetic to ferromagnetic ordering in semi-Heusler alloys Cu1-xNixMnSb with increasing Ni concentration
The magnetic properties and transition from an antiferromagnetic (AFM) to a
ferromagnetic (FM) state in semi Heusler alloys Cu1-xNixMnSb, with x < 0.3 have
been investigated in details by dc magnetization, neutron diffraction, and
neutron depolarization. We observe that for x < 0.05, the system Cu1-xNixMnSb
is mainly in the AFM state. In the region 0.05 \leq x \leq 0.2, with decrease
in temperature, there is a transition from a paramagnetic to a FM state and
below ~50 K both AFM and FM phases coexist. With an increase in Ni
substitution, the FM phase grows at the expense of the AFM phase and for x >
0.2, the system fully transforms to the FM phase. Based on the results
obtained, we have performed a quantitative analysis of both magnetic phases and
propose a magnetic phase diagram for the Cu1-xNixMnSb series in the region x <
0.3. Our study gives a microscopic understanding of the observed crossover from
the AFM to FM ordering in the studied semi Heusler alloys Cu1-xNixMnSb.Comment: 29 pages, 8 figure
Understanding the multiple magnetic structures of the intermetallic compound NdMn1.4Co0.6Si2
Magnetic phases for the intermetallic compound NdMn1.4Co0.6Si2 have been
investigated at various temperatures by dc magnetization, neutron diffraction
and neutron depolarization. Our study shows multiple magnetic phase transitions
with temperature (T) over 1.5-300 K. In agreement with dc-magnetization and
neutron depolarization results, the temperature dependence of the neutron
diffraction patterns shows five distinct regions with different magnetic
phases. These temperature regions are (i) T >= 215 K, (ii) 215 K > T >= 50 K,
(iii) 50 K > T >= 40 K, (iv) 40 K > T > 15 K, and (v) T =< 15 K. The
corresponding magnetic structures are paramagnetic, commensurate collinear
antiferromagnetic (AFM-I), incommensurate AFM (AFM-II), mixed ferromagnetic and
AFM (FM+AFM-II), and incommensurate AFM (AFM-II), respectively.Comment: 26 pages, 10 figure
Laparoscopic adjustable gastric banding – should a second chance be given?
Background:
Obesity is a chronic relapsing-remitting disease and a global pandemic, being associated with multiple comorbidities. Laparoscopic adjustable gastric banding (LAGB) is one of the safest surgical procedures used for the treatment of obesity, and even though its popularity has been decreasing over time, it still remains an option for a certain group of patients, producing considerable weight loss and improvement in obesity-associated comorbidities.
Methods:
The aim of this study was to evaluate the impact of weight loss following LAGB on obesity-associated comorbidities, and to identify factors that could predict better response to surgery, and patient sub-groups exhibiting greatest benefit. A total of 99 severely obese patients (81.2% women, mean age 44.19 ± 10.94 years, mean body mass index (BMI) 51.84 ± 8.77 kg/m2) underwent LAGB in a single institution. Results obtained 1, 2, and 5 years postoperatively were compared with the pre-operative values using SPPS software version 20.
Results:
A significant drop in BMI was recorded throughout the follow-up period, as well as in A1c and triglycerides, with greatest improvement seen 2 years after surgery (51.8 ± 8.7 kg/m2 vs 42.3 ± 9.2 kg/m2, p < 0.05, 55.5 ± 19.1 mmol/mol vs 45.8 ± 13.7 mmol/mol, p < 0.05, and 2.2 ± 1.7 mmol/l vs 1.5 ± 0.6 mmol/l). Better outcomes were seen in younger patients, with lower duration of diabetes before surgery, and lower pre-operative systolic blood pressure.
Conclusions:
Younger age, lower degree of obesity, and lower severity of comorbidities at the time of surgery can be important predictors of successful weight loss, making this group of patients the ideal candidates for LAGB
Forest edges have high conservation value for bird communities in mosaic landscapes
A major conservation challenge in mosaic landscapes is to understand how trait-specific responses to habitat edges affect bird communities, including potential cascading effects on bird functions providing ecosystem services to forests, such as pest control. Here, we examined how bird species richness, abundance and community composition varied from interior forest habitats and their edges into adjacent open habitats, within a multi-regional sampling scheme. We further analyzed variations in Conservation Value Index (CVI), Community Specialization Index (CSI) and functional traits across the forest-edge-open habitat gradient. Bird species richness, total abundance and CVI were significantly higher at forest edges while CSI peaked at interior open habitats, i.e., furthest from forest edge. In addition, there were important variations in trait-and species-specific responses to forest edges among bird communities. Positive responses to forest edges were found for several forest bird species with unfavorable conservation status. These species were in general insectivores, understorey gleaners, cavity nesters and long-distance migrants, all traits that displayed higher abundance at forest edges than in forest interiors or adjacent open habitats. Furthermore, consistently with predictions, negative edge effects were recorded in some forest specialist birds and in most open-habitat birds, showing increasing densities from edges to interior habitats. We thus suggest that increasing landscape-scale habitat complexity would be beneficial to declining species living in mosaic landscapes combining small woodlands and open habitats. Edge effects between forests and adjacent open habitats may also favor bird functional guilds providing valuable ecosystem services to forests in long-standing fragmented landscapes
Comparison of respondent-reported and sensor-recorded latrine utilization measures in rural Bangladesh: a cross-sectional study.
Background: Health improvements realized through sanitation are likely achieved through high levels of facilities utilization by all household members. However, measurements of sanitation often rely on either the presence of latrines, which does not guarantee use, or respondent-reported utilization of sanitation facilities, which is prone to response bias. Overstatement of sanitation metrics limits the accuracy of program outcome measures, and has implications for the interpretation of related health impact data. Methods: We conducted a cross-sectional study of 213 households in 14 village water, sanitation and hygiene committee clusters throughout rural Bangladesh and used a combined data- and relationship-scale approach to assess agreement between respondent-reported latrine utilization and sensor-recorded measurement. Results: Four-day household-level respondent-reported defecation averaged 28 events (inter-quartile range [IQR] 20-40), while sensor-recorded defecation averaged 17 events (IQR 11-29). Comparative analyses suggest moderately high accuracy (bias correction factor=0.84), but imprecision in the data (broad scatter of data, Pearson's r=0.35) and thus only weak concordance between measures (ρc=0.29 [95% BCa CI 0.15 to 0.43]). Conclusions: Respondent-reported latrine utilization data should be interpreted with caution, as evidence suggests use is exaggerated. Coupling reported utilization data with objective measures of use may aid in the estimation of latrine use
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