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1.
Sensors (Basel) ; 24(11)2024 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-38894431

RESUMO

In an era dominated by Internet of Things (IoT) devices, software-as-a-service (SaaS) platforms, and rapid advances in cloud and edge computing, the demand for efficient and lightweight models suitable for resource-constrained devices such as data processing units (DPUs) has surged. Traditional deep learning models, such as convolutional neural networks (CNNs), pose significant computational and memory challenges, limiting their use in resource-constrained environments. Echo State Networks (ESNs), based on reservoir computing principles, offer a promising alternative with reduced computational complexity and shorter training times. This study explores the applicability of ESN-based architectures in image classification and weather forecasting tasks, using benchmarks such as the MNIST, FashionMnist, and CloudCast datasets. Through comprehensive evaluations, the Multi-Reservoir ESN (MRESN) architecture emerges as a standout performer, demonstrating its potential for deployment on DPUs or home stations. In exploiting the dynamic adaptability of MRESN to changing input signals, such as weather forecasts, continuous on-device training becomes feasible, eliminating the need for static pre-trained models. Our results highlight the importance of lightweight models such as MRESN in cloud and edge computing applications where efficiency and sustainability are paramount. This study contributes to the advancement of efficient computing practices by providing novel insights into the performance and versatility of MRESN architectures. By facilitating the adoption of lightweight models in resource-constrained environments, our research provides a viable alternative for improved efficiency and scalability in modern computing paradigms.

2.
Nat Mater ; 23(3): 363-368, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38302742

RESUMO

Crystal lattice fluctuations, which are known to influence phase transitions of quantum materials in equilibrium, are also expected to determine the dynamics of light-induced phase changes. However, they have only rarely been explored in these dynamical settings. Here we study the time evolution of lattice fluctuations in the quantum paraelectric SrTiO3, in which mid-infrared drives have been shown to induce a metastable ferroelectric state. Crucial in these physics is the competition between polar instabilities and antiferrodistortive rotations, which in equilibrium frustrate the formation of long-range ferroelectricity. We make use of high-intensity mid-infrared optical pulses to resonantly drive the Ti-O-stretching mode at 17 THz, and we measure the resulting change in lattice fluctuations using time-resolved X-ray diffuse scattering at a free-electron laser. After a prompt increase, we observe a long-lived quench in R-point antiferrodistortive lattice fluctuations. Their enhancement and reduction are theoretically explained by considering the fourth-order nonlinear phononic interactions to the driven optical phonon and third-order coupling to lattice strain, respectively. These observations provide a number of testable hypotheses for the physics of light-induced ferroelectricity.

3.
Phys Rev Lett ; 129(12): 127601, 2022 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-36179158

RESUMO

We use an x-ray free-electron laser to study the lattice dynamics following photoexcitation with ultrafast near-UV light (wavelength 266 nm, 50 fs pulse duration) of the incipient ferroelectric potassium tantalate, KTaO_{3}. By probing the lattice dynamics corresponding to multiple Brillouin zones through the x-ray diffuse scattering with pulses from the Linac Coherent Light Source (LCLS) (wavelength 1.3 Å and <10 fs pulse duration), we observe changes in the diffuse intensity associated with a hardening of the transverse acoustic phonon branches along Γ to X and Γ to M. Using force constants from density functional theory, we fit the quasiequilibrium intensity and obtain the instantaneous lattice temperature and density of photoexcited charge carriers. The density functional theory calculations demonstrate that photoexcitation transfers charge from oxygen 2p derived π-bonding orbitals to Ta 5d derived antibonding orbitals, further suppressing the ferroelectric instability and increasing the stability of the cubic, paraelectric structure.

4.
Phys Rev Lett ; 128(15): 155301, 2022 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-35499894

RESUMO

Using femtosecond time-resolved x-ray diffraction, we investigated optically excited coherent acoustic phonons in the Weyl semimetal TaAs. The low symmetry of the (112) surface probed in our experiment enables the simultaneous excitation of longitudinal and shear acoustic modes, whose dispersion closely matches our simulations. We observed an asymmetry in the spectral line shape of the longitudinal mode that is notably absent from the shear mode, suggesting a time-dependent frequency chirp that is likely driven by photoinduced carrier diffusion. We argue on the basis of symmetry that these acoustic deformations can transiently alter the electronic structure near the Weyl points and support this with model calculations. Our study underscores the benefit of using off-axis crystal orientations when optically exciting acoustic deformations in topological semimetals, allowing one to transiently change their crystal and electronic structures.

5.
Struct Dyn ; 9(2): 024301, 2022 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-35311000

RESUMO

We report the observation of photo-induced plasmon-phonon coupled modes in the group IV-VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.

6.
Nature ; 603(7899): 52-57, 2022 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-35236977

RESUMO

All disc-accreting astrophysical objects produce powerful disc winds. In compact binaries containing neutron stars or black holes, accretion often takes place during violent outbursts. The main disc wind signatures during these eruptions are blue-shifted X-ray absorption lines, which are preferentially seen in disc-dominated 'soft states'1,2. By contrast, optical wind-formed lines have recently been detected in 'hard states', when a hot corona dominates the luminosity3. The relationship between these signatures is unknown, and no erupting system has as yet revealed wind-formed lines between the X-ray and optical bands, despite the many strong resonance transitions in this ultraviolet (UV) region4. Here we report that the transient neutron star binary Swift J1858.6-0814 exhibits wind-formed, blue-shifted absorption lines associated with C IV, N V and He II in time-resolved UV spectroscopy during a luminous hard state, which we interpret as a warm, moderately ionized outflow component in this state. Simultaneously observed optical lines also display transient blue-shifted absorption. Decomposing the UV data into constant and variable components, the blue-shifted absorption is associated with the former. This implies that the outflow is not associated with the luminous flares in the data. The joint presence of UV and optical wind features reveals a multi-phase and/or spatially stratified evaporative outflow from the outer disc5. This type of persistent mass loss across all accretion states has been predicted by radiation-hydrodynamic simulations6 and helps to explain the shorter-than-expected duration of outbursts7.

7.
Sci Total Environ ; 823: 153596, 2022 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-35122844

RESUMO

Alternaria conidia have high allergenic potential and they can trigger important respiratory diseases. Due to that and to their extensive detection period, airborne Alternaria spores are considered as a relevant airborne allergenic particle. Several studies have been developed in order to predict the human exposure to this aeroallergen and to prevent their negative effects on sensitive population. These studies revealed that some sampling locations usually have just one single Alternaria spore season while other locations generally have two seasons within the same year. However, the reasons of these two different seasonal patterns remain unclear. To understand them better, the present study was carried out in order to determine if there are any weather conditions that influence these different behaviours at different sampling locations. With this purpose, the airborne Alternaria spore concentrations of 18 sampling locations in a wide range of latitudinal, altitudinal and climate ranges of Spain were studied. The aerobiological samples were obtained by means of Hirst-Type volumetric pollen traps, and the seasonality of the airborne Alternaria spores were analysed. The optimal weather conditions for spore production were studied, and the main weather factor affecting Alternaria spore seasonality were analysed by means of random forests and regression trees. The results showed that the temperature was the most relevant variable for the Alternaria spore dispersion and it influenced both the spore integrals and their seasonality. The water availability was also a very significant variable. Warmer sampling locations generally have a longer period of Alternaria spore detection. However, the spore production declines during the summer when the temperatures are extremely warm, what splits the favourable period for Alternaria spore production and dispersion into two separate ones, detected as two Alternaria spore seasons within the same year.


Assuntos
Microbiologia do Ar , Alternaria , Alérgenos/análise , Monitoramento Ambiental , Humanos , Estações do Ano , Espanha , Esporos Fúngicos
8.
Nat Mater ; 21(1): 62-66, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-34750539

RESUMO

Symmetry plays a central role in conventional and topological phases of matter, making the ability to optically drive symmetry changes a critical step in developing future technologies that rely on such control. Topological materials, like topological semimetals, are particularly sensitive to a breaking or restoring of time-reversal and crystalline symmetries, which affect both bulk and surface electronic states. While previous studies have focused on controlling symmetry via coupling to the crystal lattice, we demonstrate here an all-electronic mechanism based on photocurrent generation. Using second harmonic generation spectroscopy as a sensitive probe of symmetry changes, we observe an ultrafast breaking of time-reversal and spatial symmetries following femtosecond optical excitation in the prototypical type-I Weyl semimetal TaAs. Our results show that optically driven photocurrents can be tailored to explicitly break electronic symmetry in a generic fashion, opening up the possibility of driving phase transitions between symmetry-protected states on ultrafast timescales.

9.
J Interpers Violence ; 37(11-12): NP9953-NP9980, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-33375875

RESUMO

In order to end and "liberate" themselves from an abusive relationship, female survivors of intimate partner violence (IPV) usually face a complex process. Although women may decide to seek help through the criminal justice system, some refuse to participate in legal proceedings against their abusers. While many studies have focused on exploring variables explaining disengagement from legal proceedings, the aim of this article is to study the impact of the process of liberation from an abusive relationship on the likelihood of disengagement (LoD) from legal proceedings. Liberation was measured through the psychosocial separation overall score and the LoD was predicted by a logistic regression model developed in a previous study in Spain. A sample of 80 women involved in legal proceedings for IPV against their ex-partners in Andalusia (Spain) participated in this study. Exploratory analyses were conducted using ANOVA and Chi-square; multiple linear regression analyses were used to study the relationship between psychosocial separation and LoD. Results showed that victims who had higher psychosocial separation from their abusers were less likely to disengage from legal proceedings against the abuser. We discuss the results in terms of practical implications like detection of women's need for specific psychological support to ease a comprehensive recovery. Training programs for legal professionals and judges in the judicial arena should use the results of this study to increase professionals' understanding of IPV and survivors' decision-making processes. This would lead to a decrease in survivors' secondary victimization, as well as decrease the frustration of legal professionals when victims disengage from legal proceedings.


Assuntos
Vítimas de Crime , Violência por Parceiro Íntimo , Vítimas de Crime/psicologia , Feminino , Humanos , Violência por Parceiro Íntimo/psicologia , Comportamento Sexual , Parceiros Sexuais , Espanha
10.
Environ Res ; 200: 111391, 2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-34058184

RESUMO

Missing data is a common problem in scientific research. The availability of extensive environmental time series is usually laborious and difficult, and sometimes unexpected failures are not detected until samples are processed. Consequently, environmental databases frequently have some gaps with missing data in it. Applying an interpolation method before starting the data analysis can be a good solution in order to complete this missing information. Nevertheless, there are several different approaches whose accuracy should be considered and compared. In this study, data from 6 aerobiological sampling stations were used as an example of environmental data series to assess the accuracy of different interpolation methods. For that, observed daily pollen/spore concentration data series were randomly removed, interpolated by using different methods and then, compared with the observed data to measure the errors produced. Different periods, gap sizes, interpolation methods and bioaerosols were considered in order to check their influence in the interpolation accuracy. The moving mean interpolation method obtained the highest success rate as average. By using this method, a success rate of the 70% was obtained when the risk classes used in the alert systems of the pollen information platforms were taken into account. In general, errors were mostly greater when there were high oscillations in the concentrations of biotic particles during consecutive days. That is the reason why the pre-peak and peak periods showed the highest interpolation errors. The errors were also higher when gaps longer than 5 days were considered. So, for completing long periods of missing data, it would be advisable to test other methodological approaches. A new Variation Index based on the behaviour of the pollen/spore season (measurement of the variability of the concentrations every 2 consecutive days) was elaborated, which allows to estimate the potential error before the interpolation is applied.


Assuntos
Pólen , Bases de Dados Factuais , Estações do Ano
11.
J Intellect Disabil Res ; 64(8): 612-628, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32573859

RESUMO

BACKGROUND: People with intellectual disabilities (IDs) seem to have a lower physical fitness (PF) than their peers without disabilities, which coincides with reduced autonomy, life expectancy and quality of life. To assess PF in these individuals, it is necessary to use appropriate tools that permit the assessment of their physical capacities taking into account their specific characteristics. The aim of this work is to study the feasibility and reliability of the Assessing Levels of Physical Activity (ALPHA)-Fit test battery for adults in a group of men and women with mild to moderate ID. METHODS: Forty-one adults with ID of both sexes, ranging in age from 20 to 60 years old, participated in the study. To identify the feasibility and reliability of the ALPHA-Fit test battery for adults, two complete assessments were done for each one of the tests included in the battery. The assessments were performed for a period of no more than 2 weeks (test-retest). An intraclass correlation coefficient was used to determinate test-retest reliability, and a mixed analysis of variance factorial was used for each of the dependent variables. Bland-Altman plots were also used to assess consistency between the two measurements. Feasibility was calculated as the percentage of people who were able to perform the tests correctly (not feasible <50%, fairly feasible 50%-75% and feasible >75%). In order to determine other psychometric properties, minimal detectable change and standard error of measurement (SEM) were also calculated. RESULTS: Of the 10 tests in the ALPHA-Fit test battery, eight were shown to be feasible. High reliability was obtained (>0.90) for the variables related to body composition. In the hand-grip test, reliability was high in the men's group but low in the women's group. Good reliability results were also found (0.80-0.89) in the dynamic sit-up test for women, but not for men. Fair reliability (0.70-0.79) was found in jump-and-reach and neck-shoulder mobility tests. The variables in the 2-km walk and agility tests indicated poor reliability. All tests showed SEM values related to high variability. However, Bland-Altman plots showed results related to lack of consistency. CONCLUSIONS: The feasibility and reliability calculations, as well as the SEM values, confirm that not all the tests of the ALPHA-Fit Test Battery for Adults are suitable for the assessment of PF in adults with ID, probably because of the complexity of the motor fitness tests. The authors emphasise the necessity of making adaptations to the protocols used or of using other tests more appropriate to the characteristics of people with mild to moderate ID.


Assuntos
Teste de Esforço/normas , Exercício Físico/fisiologia , Deficiência Intelectual/fisiopatologia , Aptidão Física/fisiologia , Psicometria/normas , Adulto , Estudos de Viabilidade , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos Testes , Adulto Jovem
12.
Psicothema ; 32(1): 40-46, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31954414

RESUMO

BACKGROUND: While the reasons female victims of gender-based intimate partner violence (GIPV) withdraw from legal proceedings continue to fuel debate, little is known about the heterogeneity of these women regarding the timing of their decision and its connection to liberating themselves from the violent relationship. METHOD: We used Analyses of Variance and Chi-squared tests to identify variables related to withdrawal from legal proceedings and variables indicating progress in the separation process related to the timing of withdrawal: in the initial or final stages of the legal proceedings. The analyses were performed in a sample of 105 women who had dropped charges. Then, we ran Binary Logistic Regression analyses to predict the risk of withdrawal during the initial stages of proceedings. RESULTS: Women withdrawing in the initial stages showed more indicators that the ending of the relationship was still incipient. The predictive model included two variables: not expecting protection from the judicial system and not applying for a protection order. CONCLUSIONS: Detachment from the relationship is essential in the complex decision surrounding withdrawal; professional action is needed that does not jeopardise recovery from GIPV.


Assuntos
Tomada de Decisões , Divórcio/psicologia , Pesar , Culpa , Violência por Parceiro Íntimo/legislação & jurisprudência , Violência por Parceiro Íntimo/psicologia , Adulto , Análise de Variância , Distribuição de Qui-Quadrado , Divórcio/estatística & dados numéricos , Escolaridade , Feminino , Humanos , Relações Interpessoais , Violência por Parceiro Íntimo/estatística & dados numéricos , Modelos Logísticos , Sistemas de Apoio Psicossocial , Espanha , Inquéritos e Questionários , Fatores de Tempo
13.
Violence Against Women ; 26(12-13): 1493-1516, 2020 10.
Artigo em Inglês | MEDLINE | ID: mdl-31662100

RESUMO

This article examines which variables predict disengagement from legal proceedings by victims of intimate partner violence in the first steps of the Spanish judicial process. We replicated a previous retrospective study with a prospective sample of 393 women. The relationships of sociodemographic, emotional, motivational, and psychological variables with procedural withdrawals were analyzed. We developed a binary logistic regression model that predicts disengagement with two variables: the contact with the abuser and the interaction between this contact and the thought of going back with him. Interesting differences between the current and the retrospective study were found. Results are discussed extensively in the conclusions.


Assuntos
Vítimas de Crime/psicologia , Violência por Parceiro Íntimo/legislação & jurisprudência , Violência por Parceiro Íntimo/psicologia , Adolescente , Adulto , Idoso , Feminino , Humanos , Modelos Logísticos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Espanha , Inquéritos e Questionários , Adulto Jovem
15.
Chemosphere ; 234: 668-681, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31234084

RESUMO

Daily fluctuations of the airborne pollen concentrations produce variations on symptomatology in allergic population. Such fluctuations are influenced by local vegetal coverage, flowering phenology, geography and climatology. Since 1991, airborne pollen of Malaga province (southern Spain) has been monitored in 7 different locations. Malaga station has been kept operational uninterruptedly throughout the studied period, while the rest of the stations only worked in periods of 2-4 years. Weekly, its pollen information is updated online to inform the population in order to prevent allergic diseases. Increasing the spatial resolution of pollen information would be very useful for allergic population living at unsampled locations. Due to the impossibility of keeping operational a high number of pollen stations covering the whole province of Malaga, the aim of this study is to create spatial models to extrapolate and forecast the pollen concentrations to Malaga province by using the concentrations registered at the capital as unique input. To do so, the relationships obtained between the airborne pollen concentrations detected at Malaga city and those detected at the other stations have been used to elaborate models for the main pollen types registered at the province. These models were spatially interpolated all over the province by using co-kriging techniques and the Compensated Thermicity Index as covariable. As result of this work, pollen distribution of the 8 most prevalent taxa has been depicted all over the whole Malaga province and an allergy alert system has been set up to extrapolate pollen information from Malaga to the whole province.


Assuntos
Poluentes Atmosféricos/análise , Poluição do Ar/estatística & dados numéricos , Alérgenos/análise , Monitoramento Ambiental/métodos , Pólen/química , Estações do Ano , Previsões , Humanos , Espanha , Análise Espaço-Temporal
16.
Environ Res ; 174: 160-169, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31077991

RESUMO

The effect of height on pollen concentration is not well documented and little is known about the near-ground vertical profile of airborne pollen. This is important as most measuring stations are on roofs, but patient exposure is at ground level. Our study used a big data approach to estimate the near-ground vertical profile of pollen concentrations based on a global study of paired stations located at different heights. We analyzed paired sampling stations located at different heights between 1.5 and 50 m above ground level (AGL). This provided pollen data from 59 Hirst-type volumetric traps from 25 different areas, mainly in Europe, but also covering North America and Australia, resulting in about 2,000,000 daily pollen concentrations analyzed. The daily ratio of the amounts of pollen from different heights per location was used, and the values of the lower station were divided by the higher station. The lower station of paired traps recorded more pollen than the higher trap. However, while the effect of height on pollen concentration was clear, it was also limited (average ratio 1.3, range 0.7-2.2). The standard deviation of the pollen ratio was highly variable when the lower station was located close to the ground level (below 10 m AGL). We show that pollen concentrations measured at >10 m are representative for background near-ground levels.


Assuntos
Monitoramento Ambiental , Pólen , Alérgenos , Austrália , Europa (Continente) , Humanos , Estações do Ano , Manejo de Espécimes
17.
J Antimicrob Chemother ; 74(5): 1357-1362, 2019 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-30753573

RESUMO

BACKGROUND: HIV-2 is a neglected virus despite estimates of 1-2 million people being infected worldwide. The virus is naturally resistant to some antiretrovirals used to treat HIV-1 and therapeutic options are limited for patients with HIV-2. METHODS: In this retrospective observational study, we analysed all HIV-2-infected individuals treated with integrase strand transfer inhibitors (INSTIs) recorded in the Spanish HIV-2 cohort. Demographics, treatment modalities, laboratory values, quantitative HIV-2 RNA and CD4 counts as well as drug resistance were analysed. RESULTS: From a total of 354 HIV-2-infected patients recruited by the Spanish HIV-2 cohort as of December 2017, INSTIs had been given to 44, in 18 as first-line therapy and in 26 after failing other antiretroviral regimens. After a median follow-up of 13 months of INSTI-based therapy, undetectable viraemia for HIV-2 was achieved in 89% of treatment-naive and in 65.4% of treatment-experienced patients. In parallel, CD4 gains were 82 and 126 cells/mm3, respectively. Treatment failure occurred in 15 patients, 2 being treatment-naive and 13 treatment-experienced. INSTI resistance changes were recognized in 12 patients: N155H (5), Q148H/R (3), Y143C/G (3) and R263K (1). CONCLUSIONS: Combinations based on INSTIs are effective and safe treatment options for HIV-2-infected individuals. However, resistance mutations to INSTIs are selected frequently in failing patients, reducing the already limited treatment options.


Assuntos
Infecções por HIV/tratamento farmacológico , Inibidores de Integrase de HIV/uso terapêutico , HIV-2/efeitos dos fármacos , Adolescente , Adulto , Contagem de Linfócito CD4 , Farmacorresistência Viral/genética , Feminino , Inibidores de Integrase de HIV/farmacologia , Humanos , Masculino , Testes de Sensibilidade Microbiana , Pessoa de Meia-Idade , Mutação , RNA Viral/sangue , Estudos Retrospectivos , Espanha , Falha de Tratamento
18.
Neurol Sci ; 40(2): 261-268, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30368695

RESUMO

OBJECTIVE: Neurological symptoms in patients with cat-scratch disease (CSD) have been rarely reported. The aim of this study is to analyze the frequency of neurological CSD (NCSD) and describe the disease clinical presentation, management and outcome. MATERIAL AND METHODS: We retrospectively selected patients with a CSD syndrome and Bartonella IgG titers > 1:256. Data regarding epidemiological, clinical, management, and follow-up features were analyzed and discussed. A comparison between NCSD and non-neurological CSD (NNCSD) was established. RESULTS: Thirty-nine CSD patients were selected. NCSD frequency was 10.25%. No children were found affected in the NCSD group. A 65.7% of NNCSD and the entirety of the NCSD group had a history of cat exposure. Immunosuppression was only present in the NNCSD group (8.6%). NCSD presentations were as follows: isolated aseptic meningitis (25%), neuroretinitis (50%), and isolated optic neuritis (25%). A greater proportion of patients in the NCSD group had fever and raised levels of acute phase reactants and white blood cells. 85.7% of NNCSD had a complete recovery, whereas only 50% of the NCSD patients experienced a full recovery. CONCLUSION: NCSD may be a distinctive group compared to NNCSD due to its later age of presentation, the more intense systemic response, and the poorer outcome.


Assuntos
Bartonella henselae , Doença da Arranhadura de Gato/epidemiologia , Doença da Arranhadura de Gato/fisiopatologia , Adolescente , Adulto , Idoso , Antibacterianos/uso terapêutico , Doença da Arranhadura de Gato/diagnóstico , Doença da Arranhadura de Gato/terapia , Feminino , Fundo de Olho , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Resultado do Tratamento , Adulto Jovem
19.
Phys Rev Lett ; 120(10): 105501, 2018 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-29570335

RESUMO

Long wavelength vibrational modes in the ferromagnetic semiconductor Ga_{0.91}Mn_{0.09}As are investigated using time resolved x-ray diffraction. At room temperature, we measure oscillations in the x-ray diffraction intensity corresponding to coherent vibrational modes with well-defined wavelengths. When the correlation of magnetic impurities sets in, we observe the transition of the lattice into a disordered state that does not support coherent modes at large wavelengths. Our measurements point toward a magnetically induced broadening of long wavelength vibrational modes in momentum space and their quasilocalization in the real space. More specifically, long wavelength vibrational modes cannot be assigned to a single wavelength but rather should be represented as a superposition of plane waves with different wavelengths. Our findings have strong implications for the phonon-related processes, especially carrier-phonon and phonon-phonon scattering, which govern the electrical conductivity and thermal management of semiconductor-based devices.

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