3,842 research outputs found
Constant of Motion for several one-dimensional systems and outlining the problem associated with getting their Hamiltonians
The constants of motion of the following systems are deduced: a relativistic
particle with linear dissipation, a no-relativistic particle with a time
explicitly depending force, a no-relativistic particle with a constant force
and time depending mass, and a relativistic particle under a conservative force
with position depending mass. The problem of getting the Hamiltonian for these
systems is determined by getting the velocity as an explicit function of
position and generalized linear momentum, and this problem can be solved a
first approximation for the first above system.Comment: 15 pages, Te
When tanß meets all the mixing angles
Models with two-Higgs-doublets and natural flavour conservation contain as a physical parameter. We offer here a generalization of a recently proposed idea where only the Cabibbo angle, , was related to by virtue of the dihedral symmetry group. The original proposal consisted of a massless first generation of quarks and no mixing with the third generation. In our case, through the addition of a third Higgs doublet with a small vacuum-expectation-value but very large masses, thus later decoupling, all quarks become massive and quark mixing is fully reproduced. In fact, all quark mixing angles are expressed in terms of and one recovers trivial mixing in the limit . We also explore the consequences in lepton mixing by adopting a type I seesaw mechanism with three heavy right-handed neutrinos
Variable speed liquid chiller drop-in modeling for predicting energy performance of R1234yf as low-GWP refrigerant
This paper presents a model for a variable-speed liquid chiller integrating a compressor model based on Buckingham π-theorem to accurately predict the system performance when R134a is replaced with R1234yf, using a wide range of data obtained from an experimental setup. Relevant variables such as temperature, pressure, mass and volumetric flow rates, compressor power consumption and rotation speed were measured at several positions along the refrigeration and secondary circuits and were used to validate the developed model. Model results show that cooling capacity and power consumption predicted values are in good agreement with experimental data, within ±5%, being slightly higher for the deviation obtained for R134a than for R1234yf. Moreover, model results indicate that R1234yf has a reduction of coefficient of performance (COP) compared with R134a (between 2 and 11.3%), and that R1234yf COP reduction is diminished at intermediate volumetric flow rate and higher inlet temperature for the evaporator secondary fluid, respectively. On the other hand, an environmental analysis based on TEWI (total equivalent warming impact) method showed that direct emissions are almost negligible for R1234yf. However, there are no environmental benefits in terms of indirect greenhouse gas emissions using R1234yf without system modifications (as for instance the addition of internal heat exchanger or R1234yf new design components), which are required to reduce the liquid chiller climate change contribution using it as low GWP alternative in comparison with the typically used R134a refrigerant
External stimuli help restore post-partum ovarian activity in Pelibuey sheep
Post-partum anestrus is a problem on farms, and its duration depends on the frequency and intensity of suckling which affects reproduction and production efficiency to become a determining economic factor. The aim of this study was to determine the post-partum reproductive response in ewe to a "male effect" with an ovulation induction protocol of five days using progesterone and the application of a metabolic restorative (MR; Metabolase ®). One hundred and twenty females were randomly assigned to one of four treatments: T1: Continuous suckling (CS; n = 29), T2: CS + MR (n = 29), T3: CS + Male Effect (ME; n = 32), and T4: CS + MR + ME. The percentage of females in ovulation, weight changes among females and lambs, the onset of estrus, calving, fecundity, and prolificacy were also determined. The ovulation percentage was higher in CS + ME and CS + MR + ME (75.0 and 73.3%) than in the other treatments. Weight changes in females and lambs were different among periods. The onset of estrus was similar for CS and CS + MR (25.9 ± 1.9 and 25.7 ± 0.7 h, respectively). The calving percentage was higher for CS + MR (86.2%) than other treatments. Male presence positively affected the postpartum cyclic ovarian re-establishment and the metabolic restorative could even improve the fertility of hair ewes in continuous suckling with similar hormone protocolKeywords: Male effect, metabolic stimulation, post-partum anestru
Extraction of 2′-O-apiosyl-6′-O-crotonic acid-betanin from the ayrampo seed (Opuntia soehrensii) cuticle and its use as an emitting layer in an organic light-emitting diode
The molecule 2′-O-apiosyl-6′-O-crotonic acid-betanin (called Achkiy) was obtained after an ecofriendly and low-cost purification process of the extract from the ayrampo seed cuticle. Results from EDS give us an idea of the organic elements present in the ayrampo cuticle layer composed of carbon, oxygen and nitrogen. Further characterization analysis of ayrampo extract by Fourier Transform Infrared Spectrophotometry (FTIR) corroborated the presence of characteristic functional groups corresponding to carboxyl, carbonyls, hydroxyls and secondary amines. On the other hand, we have confirmed by absortion peak the glucose, apiosyl, crotonic acid and betanin at 227 nm, 276 nm, 291 nm and 534 nm bands respectively. Mass Spectrometry (MS) characterization was used finally to identify the electroactive Achkiy molecule. This molecule was tested in an Organic Light Emitting Diode (OLED) achieving a luminance of 4.8 Cd m when bias voltage of 16.5 V and a current of 34.1 mA was applied. In addition, the irradiance generated by the Achkiy layer reaches a value of ≈ 113.3 μW m emitting light with a λ ≈ 390.10 nm. These preliminary results report an interesting molecule extracted from a natural pigment wich emits light in the blue region
Comparative evaluation of R1234yf, R1234ze(E) and R450A as alternatives to R134a in a variable speed reciprocating compressor
A comparative energetic evaluation of R1234yf, R1234ze(E) and R450A as alternatives to R134a in a
variable speed compressor is carried out. A compressor model based on dimensionless numbers was
obtained using the Buckingham
p
-theorem, which was validated with experimental data; showing that
the prediction error of the model is lower than
±
10% and
±
2 K for temperature. The experimental data
were obtained by testing R134a, R1234yf, R1234ze(E) and R450A for a wide range of operating condi-
tions. Results obtained with the validated model, show that the dimensionless approach provides a
similar estimation of energy parameters compared with the experimental results, such as power con-
sumption, refrigerant mass
fl
ow rate, cooling capacity, COP, discharge temperature and compressor ef-
fi
ciencies for each refrigerant tested using the dimensionless approach proposed. The comparative
evaluation of the compressor predictions shows a reduction in the cooling capacity obtained with
R1234yf, R450A and R1234ze(E), in comparison with R134a. Also, COP values for R1234yf, R450A, and
R1234ze(E) are lower than those obtained from R134a. Finally, results shows that the dimensionless
correlation compressor model can be used to predict the performance of other reciprocating compres-
sors, at similar operating conditions for a wide range of compressor rotation speed, with a reasonable
accuracy.The authors thankfully acknowledge to the "Consejo Nacional deCiencia y Tecnología (CONACYT)” for their support to this study, and to the “Ministerio de Educación, Cultura y Deporte” (Grant number FPU12/02841) for sponsoring this work through
“Becas y Contratosde Formación de Profesorado Universitario del Programa Nacional
de Formación de Recursos Humanos de Investigación del ejercicio
2012”
Effects of cytomegalovirus infection in human neural precursor cells depend on their differentiation state
© 2015, Journal of NeuroVirology, Inc. Cytomegalovirus (CMV) is the most common cause of congenital infection in developed countries and a major cause of neurological disability in children. Although CMV can affect multiple organs, the most important sequelae of intrauterine infection are related to lesions of the central nervous system. However, little is known about the pathogenesis and the cellular events responsible for neuronal damage in infants with congenital infection. Some studies have demonstrated that neural precursor cells (NPCs) show the greatest susceptibility to CMV infection in the developing brain. We sought to establish an in vitro model of CMV infection of the developing brain in order to analyze the cellular events associated with invasion by this virus. To this end, we employed two cell lines as a permanent source of NPC, avoiding the continuous use of human fetal tissue, the human SK-N-MC neuroblastoma cell line, and an immortalized cell line of human fetal neural origin, hNS-1. We also investigated the effect of the differentiation stage in relation to the susceptibility of these cell lines by comparing the neuroblastoma cell line with the multipotent cell line hNS-1. We found that the effects of the virus were more severe in the neuroblastoma cell line. Additionally, we induced hNS-1 to differentiate and evaluated the effect of CMV in these differentiated cells. Like SK-N-MC cells, hNS-1-differentiated cells were also susceptible to infection. Viability of differentiated hNS-1 cells decreased after CMV infection in contrast to undifferentiated cells. In addition, differentiated hNS-1 cells showed an extensive cytopathic effect whereas the effect was scarce in undifferentiated cells. We describe some of the effects of CMV in neural stem cells, and our observations suggest that the degree of differentiation is important in the acquisition of susceptibility.CONACYT (CB16782 and #120452), PROMEP (103.5/10/7697), and FAI-UASLP (C12-FAI-03-62.62).Peer Reviewe
Exploring long COVID condition in Latin America: Its impact on patients’ activities and associated healthcare use
"Background: Studies exploring long COVID condition (LCC) in low- and
middle-income countries are scarce. Further characterization of LCC patients
experiencing activity limitations and their associated healthcare use is needed.
This study aimed to describe LCC patients’ characteristics, its impact on activities,
and associated healthcare use in Latin America (LATAM).
Participants: Individuals who (cared for someone or) had COVID-19 and could
read, write, and comprehend Spanish and lived in a LATAM country were invited
to complete a virtual survey. Sociodemographic characteristics, COVID-19 and
LCC symptoms, activity limitations, and healthcare use.
Results: Data from 2,466 people from 16 countries in LATAM were analyzed
(females = 65.9%; mean age of 39.5 ± 53.3 years). 1,178 (48%) of the respondents
had LCC symptoms (≥3 months). These were more likely to have COVID-19 earlier
in the pandemic, were older, had no COVID vaccines, had more comorbidities,
needed supplementary oxygen, and reported significantly more COVID-19
symptoms during the infectious period. 33% of the respondents visited a primary
care provider, 13% went to the emergency department, 5% were hospitalized,
21% visited a specialist, and 32% consulted ≥1 therapist for LCC symptoms
mainly extreme fatigue, sleep difficulties, headaches, muscle or joint pain, and
shortness of breath with activity. The most consulted therapists were respiratory
therapists (15%) and psychologists (14%), followed by physical therapists (13%),
occupational therapists (3%), and speech pathologists (1%). One-third of LCC
respondents decreased their regular activities (e.g., work, school) and 8% needed
help with activities of daily living (ADLs). LCC respondents who reduced their
activities reported more difficulty sleeping, chest pain with activity, depression,
and problems with concentration, thinking, and memory, while those who
needed help with ADLs were more likely to have difficulty walking, and shortness
of breath at rest. Approximately 60% of respondents who experienced activity
limitations sought a specialist and 50% consulted therapists. Conclusions and relevance: Results supported previous findings in terms of the
LCC demographics, and provided insight into LCC impact on patients’ activities
and healthcare services used in LATAM. This information is valuable to inform
service planning and resource allocation in alignment with the needs of this
population.
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