RESUMEN
An increase in the number of transmit antennas (M) poses an equivalent rise in the number of Radio Frequency (RF) chains associated with each antenna element, particularly in digital beamforming. The chain exhibits a substantial amount of power consumption accordingly. Hence, to alleviate such problems, one of the potential solutions is to reduce the number of RFs or to minimize their power consumption. In this paper, low-resolution Digital to Analogue Conversion (DAC) and transmit antenna selection at the downlink are evaluated to favour reducing the total power consumption and achieving energy efficiency in mMIMO with reasonable complexity. Antenna selection and low-resolution DAC techniques are proposed to leverage massive MIMO systems in free space and Close In (CI) path-loss models. The simulation results show that the power consumption decreases with antenna selection and low-resolution DAC. Then, the system achieves more energy efficiency than without low-resolution of DAC and full array utilization.
Asunto(s)
Computadores , Ondas de Radio , Simulación por ComputadorRESUMEN
The nanoscale morphology of photoactive hybrid heterojunctions plays a key role in the performances of hybrid solar cells. In this work, the heterojunctions consist of a nanocolumnar TiO2 surface covalently grafted with a monolayer of poly(3-hexylthiophene) (P3HT) functionalized with carboxylic groups (-COOH). Through a joint analysis of the photovoltaic properties at the nanoscale by photoconductive-AFM (PC-AFM) and surface photovoltage imaging, we investigated the physical mechanisms taking place locally during the photovoltaic process and the correlation to the nanoscale morphology. A down-shift of the vacuum level of the TiO2 surface upon grafting was measured by Kelvin probe force microscopy (KPFM), evidencing the formation of a dipole at the TiO2/P3HT-COOH interface. Upon in situ illumination, a positive photovoltage was observed as a result of the accumulation of photogenerated holes in the P3HT layer. A positive photocurrent was recorded in PC-AFM measurements, whose spatial mapping was interpreted consistently with the corresponding KPFM analysis, offering a correlated analysis of interest from both a theoretical and material design perspective.
RESUMEN
A tri-dimensional interweaving kinked silicon nanowires (k-SiNWs) assembly, with a Ni current collector co-integrated, is evaluated as electrode configuration for lithium ion batteries. The large-scale fabrication of k-SiNWs is based on a procedure for continuous metal assisted chemical etching of Si, supported by a chemical peeling step that enables the reuse of the Si substrate. The kinks are triggered by a simple, repetitive etch-quench sequence in a HF and H2O2-based etchant. We find that the inter-locking frameworks of k-SiNWs and multi-walled carbon nanotubes exhibit beneficial mechanical properties with a foam-like behavior amplified by the kinks and a suitable porosity for a minimal electrode deformation upon Li insertion. In addition, ionic liquid electrolyte systems associated with the integrated Ni current collector repress the detrimental effects related to the Si-Li alloying reaction, enabling high cycling stability with 80% capacity retention (1695 mAh/gSi) after 100 cycles. Areal capacities of 2.42 mAh/cm2 (1276 mAh/gelectrode) can be achieved at the maximum evaluated thickness (corresponding to 1.3 mgSi/cm2). This work emphasizes the versatility of the metal assisted chemical etching for the synthesis of advanced Si nanostructures for high performance lithium ion battery electrodes.
RESUMEN
Extracellular microenvironment is highly dynamic where spatiotemporal regulation of cell-instructive cues such as matrix topography tightly regulates cellular behavior. Recapitulating dynamic changes in stimuli-responsive materials has become an important strategy in regenerative medicine to generate biomaterials which closely mimic the natural microenvironment. Here, light responsive liquid crystal polymer networks are used for their adaptive and programmable nature to form hybrid surfaces presenting micrometer scale topographical cues and changes in nanoscale roughness at the same time to direct cell migration. This study shows that the cell speed and migration patterns are strongly dependent on the height of the (light-responsive) micrometer scale topographies and differences in surface nanoroughness. Furthermore, switching cell migration patterns upon in situ temporal changes in surface nanoroughness, points out the ability to dynamically control cell behavior on these surfaces. Finally, the possibility is shown to form photoswitchable topographies, appealing for future studies where topographies can be rendered reversible on demand.
RESUMEN
Ferroelectric materials are important components of sensors, actuators and non-volatile memories. However, possible device configurations are limited due to the need to provide screening charges to ferroelectric interfaces to avoid depolarization. Here we show that, by alternating ferroelectric and semiconducting nanowires over an insulating substrate, the ferroelectric dipole moment can be stabilized by injected free charge carriers accumulating laterally in the neighboring semiconducting nanowires. This lateral electrostatic coupling between ferroelectric and semiconducting nanowires offers new opportunities to design new device architectures. As an example, we demonstrate the fabrication of an elementary non-volatile memory device in a transistor-like configuration, of which the source-drain current exhibits a typical hysteretic behavior with respect to the poling voltage. The potential for size reduction intrinsic to the nanostructured hybrid layer offers opportunities for the development of strongly miniaturized ferroelectric and piezoelectric devices.
RESUMEN
We study the interaction between an AFM tip and a soft viscoelastic surface. Using a multifrequency method we measure the amplitude-dependence of the cantilever dynamic force quadratures, which clearly show the effect of finite relaxation time of the viscoelastic surface. A model is introduced which treats the tip and surface as a two-body dynamic problem with a nonlinear interaction depending on their separation. We find good agreement between simulations of this model and experimental data on polymer blend samples for a variety of materials and measurement conditions.
RESUMEN
BACKGROUND: Cryptosporidiosis is an important cause for chronic diarrhea and death in HIV/AIDS patients. Among common Cryptosporidium species in humans, C. parvum is responsible for most zoonotic infections in industrialized nations. Nevertheless, the clinical significance of C. parvum and role of zoonotic transmission in cryptosporidiosis epidemiology in developing countries remain unclear. METHODOLOGY/PRINCIPAL FINDINGS: In this cross-sectional study, 520 HIV/AIDS patients were examined for Cryptosporidium presence in stool samples using genotyping and subtyping techniques. Altogether, 140 (26.9%) patients were positive for Cryptosporidium spp. by PCR-RFLP analysis of the small subunit rRNA gene, belonging to C. parvum (92 patients), C. hominis (25 patients), C. viatorum (10 patients), C. felis (5 patients), C. meleagridis (3 patients), C. canis (2 patients), C. xiaoi (2 patients), and mixture of C. parvum and C. hominis (1 patient). Sequence analyses of the 60 kDa glycoprotein gene revealed a high genetic diversity within the 82 C. parvum and 19 C. hominis specimens subtyped, including C. parvum zoonotic subtype families IIa (71) and IId (5) and anthroponotic subtype families IIc (2), IIb (1), IIe (1) and If-like (2), and C. hominis subtype families Id (13), Ie (5), and Ib (1). Overall, Cryptosporidium infection was associated with the occurrence of diarrhea and vomiting. Diarrhea was attributable mostly to C. parvum subtype family IIa and C. hominis, whereas vomiting was largely attributable to C. hominis and rare Cryptosporidium species. Calf contact was identified as a significant risk factor for infection with Cryptosporidium spp., especially C. parvum subtype family IIa. CONCLUSIONS/SIGNIFICANCE: Results of the study indicate that C. parvum is a major cause of cryptosporidiosis in HIV-positive patients and zoonotic transmission is important in cryptosporidiosis epidemiology in Ethiopia. In addition, they confirm that different Cryptosporidium species and subtypes are linked to different clinical manifestations.
Asunto(s)
Síndrome de Inmunodeficiencia Adquirida/complicaciones , Criptosporidiosis/epidemiología , Criptosporidiosis/parasitología , Cryptosporidium/clasificación , Cryptosporidium/aislamiento & purificación , Variación Genética , Adolescente , Adulto , Anciano , Antígenos de Protozoos/genética , Niño , Preescolar , Estudios Transversales , Cryptosporidium/genética , ADN Protozoario/química , ADN Protozoario/genética , ADN Ribosómico/genética , Etiopía/epidemiología , Heces/parasitología , Femenino , Genotipo , Glicoproteínas/genética , Humanos , Lactante , Masculino , Persona de Mediana Edad , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , Análisis de Secuencia de ADN , Adulto JovenRESUMEN
We demonstrate the design of a multifunctional organic layer by the rational combination of nanosized regions of two functional polymers. Instead of relying on a spontaneous and random phase separation process or on the tedious synthesis of block copolymers, the method involves the nanomolding of a first component, followed by the filling of the resulting open spaces by a second component. We apply this methodology to fabricate organic nonvolatile memory diodes of high density. These are built by first creating a regular array of ferroelectric nanodots by nanoimprint lithography, followed by the filling of the trenches separating the ferroelectric nanodots with a semiconducting polymer. The modulation of the current in the semiconductor by the polarization state of the ferroelectric material is demonstrated both at the scale of a single semiconductor channel and in a microscopic device measuring about 80,000 channels in parallel, for voltages below ca. 2 V. The fabrication process, which combines synergetically orthogonal functional properties with a fine control over their spatial distribution, is thus demonstrated to be efficient over large areas.
RESUMEN
Mass balance modeling was used to apportion previously measured carbon monoxide and respirable particle exposures of women preparing coffee during Ethiopian coffee ceremonies. The coffee ceremony generates smoke indoors from the use of charcoal and incense. This creates inhalation exposures, particularly for the women preparing the coffee. Understanding the health risks associated with this practice will be improved with knowledge of the relative contribution to combustion byproduct exposures from the different sources. Source fingerprints were developed in the laboratory for carbon monoxide and respirable particle emissions from charcoal and incense. A mass balance model determined that the majority of the carbon monoxide exposures were from charcoal use and that the respirable particle exposures were approximately half from incense and half from charcoal. Efforts to decrease health risks from these exposures must be directed by Ethiopian cultural stakeholders who understand the exposure conditions, the health risks, and the societal context.
Asunto(s)
Monóxido de Carbono , Exposición a Riesgos Ambientales , Material Particulado , Contaminación del Aire Interior , Monóxido de Carbono/efectos adversos , Carbón Orgánico , Café , Culinaria , Características Culturales , Etiopía , Femenino , Humanos , Modelos Teóricos , Material Particulado/efectos adversosRESUMEN
The unique Ethiopian cultural tradition of the coffee ceremony increases inhalation exposures to combustion byproducts. This pilot study evaluated exposures to particulate matter and carbon monoxide in ten Addis Ababa homes during coffee ceremonies. For coffee preparers the geometric mean (57 µg/m³) and median (72 µg/m³) contributions to an increase in a 24-hour time-weighted average exposure were above World Health Organization (WHO) guidelines. At 40% of the study sites the contribution to the 24-hour average exposure was greater than twice the WHO guideline. Similar exposure increases existed for ceremony participants. Particulate matter concentrations may be related to the use of incense during the ceremony. In nearly all homes the WHO guideline for a 60-minute exposure to carbon monoxide was exceeded. Finding control measures to reduce these exposures will be challenging due to the deeply engrained nature of this cultural practice and the lack of availability of alternative fuels.
Asunto(s)
Contaminación del Aire Interior/estadística & datos numéricos , Monóxido de Carbono/análisis , Conducta Ceremonial , Café , Exposición por Inhalación/estadística & datos numéricos , Material Particulado/análisis , Adolescente , Adulto , Contaminación del Aire Interior/análisis , Carbón Orgánico , Culinaria/métodos , Etiopía , Femenino , Vivienda , Humanos , Exposición por Inhalación/análisis , Masculino , Persona de Mediana Edad , Proyectos Piloto , Humo/análisis , Adulto JovenRESUMEN
Food safety is an important public health issue in the U.S. Eating at restaurants and other food service facilities increasingly has been associated with food borne disease outbreaks. Food safety training and certification of food mangers has been used as a method for reducing food safety violations at food service facilities. However, the literature is inconclusive about the effectiveness of such training programs for improving food safety and protecting consumer health. The purpose of this study was to examine the effect of food manger training on reducing food safety violations. We examined food inspection reports from the Toledo/Lucas County Health Department (Ohio) from March 2005 through February 2006 and compared food hygiene violations between food service facilities with certified and without certified food managers. We also examined the impact on food safety of a food service facility being part of a larger group of facilities.Restaurants with trained and certified food managers had significantly fewer critical food safety violations but more non-critical violations than restaurants without certified personnel. Institutional food service facilities had significantly fewer violations than restaurants, and the number of violations did not differ as a function of certification. Similarly, restaurants with many outlets had significantly fewer violations than restaurants with fewer outlets, and training was not associated with lower numbers of violations from restaurants with many outlets. The value of having certified personnel was only observed in independent restaurants and those with few branches. This information may be useful in indicating where food safety problems are most likely to occur. Furthermore, we recommend that those characteristics of institutional and chain restaurants that result in fewer violations should be identified in future research, and efforts made to apply this knowledge at the level of individual restaurants.
RESUMEN
BACKGROUND: Body mass index (BMI) is a commonly used anthropometric measurement to estimate the level of nutritional indices (underweight/overweight) of adolescents and adults. Knowledge of the factors affecting BMI is essential for developing intervention programs. This study was conducted to measure BMI and determine the socioeconomic and demographic factors affecting the relative weight of adolescents living in rural districts in Ethiopia. METHODS: A randomized cross-sectional study of 425 adolescent students living in the Ambo region of Ethiopia was conducted. A pre-tested questionnaire was used to collect the socioeconomic and demographic status of the participants. BMI (weight/height(2), kg/m(2)) was measured and used as index of relative weight. Data were analyzed using SPSS version 15. A stepwise backward logistic regression analysis was applied to identify the major determinant abnormal weight of the adolescents while controlling for co-linearity. RESULTS: The prevalence of underweight was 27.2% with male preponderance. The proportion of normal weight females was higher than that of males. There was no significant difference in the proportion of overweight males and females. Age, number of meals, parental education level, source of food, and number of cattle owned were correlated with being underweight. After adjusting for confounding variables only being a member of the younger age group (AOR=1.99; 95% CI=1.01 to 3.57), source of food (AOR=2.4; 95% CI=1.24 to 4.74), and a greater number of cattle owned (AOR=4.9; 95% CI=1.27 to 19.28 were positively correlated with being underweight. CONCLUSION: Younger age adolescents, those who come from homes with no or few cattle, and their parents purchased food were likely to be underweight. This study will help local governments, educators and community groups develop programs to assist underweight adolescents attending schools.
RESUMEN
Food service workers conduct informal inspections of food service operations to ensure that food contamination does not occur. This activity requires proper lighting. Compliance with lighting standards is usually assessed by a qualitative, visual inspection method. Recent studies suggest, however, that qualitative inspections only minimally reduce risks of foodborne-disease outbreaks. To evaluate the efficacy of qualitative lighting level assessments, this study quantitatively measured lighting in walk-in coolers and at food preparation counters in 57 food service establishments. Measurements were conducted alongside regular sanitarian inspections. Of the 55 walk-in coolers evaluated, 12 had fluorescent and 43 had incandescent lighting. The geometic mean (GM) light level at the center of coolers with fluorescent lighting was 15.3 foot-candles (ft-c) (range: 6.4-85.5). Seventy-five percent of these coolers met the standard of 10 ft-c. The GM level at the center of coolers with incandescent lighting was 3.43 ft-c (range: 1.0-16.7). Seven percent of the incandescently lit coolers met the standard. Inadequate cooler illumination was indicated on only four sanitarian inspection reports. The GM level at 185 food preparation counters was 38.7 ft-c (range: 2.9-196.8). At 47 percent of the establishments, no counters met the 50 ft-c standard. Twenty-three percent of the establishments met the standard at all evaluated counters. Inadequate counter illumination was noted only once by a sanitarian. Qualitative assessments did not identify most of the lighting standard violations. Additional training and integration of quantitative assessments into inspections are warranted. Fluorescent lighting produced significantly higher light levels and pass rates in coolers and should become the lighting type of choice. Finally, gaps in the standards were identified and should be addressed.
Asunto(s)
Contaminación de Alimentos/prevención & control , Inspección de Alimentos/métodos , Servicios de Alimentación/normas , Iluminación , Microbiología de Alimentos/normas , HumanosRESUMEN
The prevalence and distribution of Cryptosporidium spp. in the fecal droppings of the free-living waterfowl Canada geese were examined at 13 sites in Ohio and Illinois. On the basis of the analysis of the small-subunit rRNA gene by PCR, followed by restriction fragment length polymorphism analysis and DNA sequencing, 49 (23.4%) of 209 fecal specimens collected from 10 sites (76.9%) were positive for Cryptosporidium spp. The following five Cryptosporidium species and genotypes were identified: Cryptosporidium goose genotype I (in 36 specimens), Cryptosporidium goose genotype II (in 9 specimens), Cryptosporidium duck genotype (in 1 specimen), Cryptosporidium parvum (in 4 specimens), and C. hominis (in 2 specimens). Cryptosporidium goose genotype I was the most prevalent parasite and was found at all five Cryptosporidium-positive sites in Ohio and at four of five positive sites in Illinois, followed by Cryptosporidium goose genotype II, which was found at two of five positive sites in Ohio and at four of five positive sites in Illinois. Cryptosporidium goose genotype II was detected for the first time, and it is phylogenetically related to goose genotype I and the duck genotype. All three genotypes have not so far been reported in humans, and their pathogenicity in geese has not been determined. Only 10.2% of the Cryptosporidium-positive specimens had C. parvum and C. hominis. The results of this study indicate that Canada geese might only serve as accidental carriers of cryptosporidia infectious to humans and probably play a minor role in the animal-to-human transmission cycle of the pathogen.
Asunto(s)
Cryptosporidium/aislamiento & purificación , Gansos/parasitología , Adaptación Fisiológica , Animales , Secuencia de Bases , Cryptosporidium/clasificación , Cryptosporidium/genética , Heces/microbiología , Datos de Secuencia Molecular , FilogeniaRESUMEN
Canada geese are increasingly abundant in Ohio, with large nesting populations throughout the state, and goose feces contaminate grassy areas and pavements in many public, commercial, and residential sites. In 1999 the authors found a high prevalence of Giardia, Campylobacter, and especially Cryptosporidium in collected feces of Canada geese. The purpose of this follow-up study was to survey known Canada geese sites in three counties in Ohio (Lucas, Ottawa, and Wood) and to determine the prevalence of sites testing positive for Cryptosporidium. The sites included golf courses, cemeteries, public parks, and health care and teaching facilities. At each of 11 sites, 12 goose feces of wet and loose appearance were collected and manually compressed into one composite sample representing that site. The samples were tested for Cryptosporidium with a sensitive monoclonal enzyme immunoassay (EIA) method. In 2000 and 2001, nine of 11 sites (81.8 percent) and nine of 10 sites (90 percent), respectively, were positive for Cryptosporidium. The species or genotypes of Cryptosporidium found in the geese feces and their potential to infect humans is unknown. A survey of the literature indicates, however, that while C. parvum (human genotype) is the main cause of cryptosporidiosis in humans, C. parvum (zoonotic genotypes), C. meleagridis (bird genotype), and C. felis (cat genotype) have occasionally been isolated from infected people. Further research is required to define the public health importance of Cryptosporidium in feces of Canada geese and other bird species.
Asunto(s)
Cryptosporidium/aislamiento & purificación , Heces/parasitología , Gansos/parasitología , Animales , Humanos , Michigan , OhioRESUMEN
Cooking processes at food service operations release fumes that present risks of food contamination, fire, and employee exposure to hazardous chemicals. Local exhaust ventilation in the form of kitchen hoods is commonly used to control these risks. State codes often refer to the need for adequate ventilation, but hoods are not an explicit point on most inspection sheets and are rarely quantitatively assessed to determine if flow rates meet recommended levels. For this article, the flow rates of 89 hoods in 60 restaurants were measured and compared with appropriate flow rate guidelines. It was found that 39 percent of the hoods met the guidelines of the American Conference of Governmental Industrial Hygienists and 24 percent met the guidelines of the American Society of Heating, Refrigerating and Air-Conditioning Engineers. Inspecting sanitarians identified inadequate flow rates in less than 4 percent of the cases. Hoods used to control heavy-duty operations such as upright broilers, charbroilers, and woks had the lowest pass rate, 18 percent. The researchers also graded the hoods in terms of cleanliness. These ratings did not correlate with hood cleanliness notes on the sanitarians' inspection reports. Overall risks from cooking fumes could be reduced by regular systematic inspections of kitchen hoods, with hoods perhaps included as an independent item on inspection sheets. Quantitative assessment of flow rates is time consuming and is probably not feasible for all inspections. Periodic inspections of hoods on heavy-duty operations could be a workable way to reduce risks.