Nonlinear dynamics of a single-gap terahertz split-ring resonator under electromagnetic radiation.

Research into metasurfaces is developing rapidly and is topical due to their importance and applications in various fields such as communications, cryptography, and sensing, to name a few. These materials are artificially engineered to manipulate/control electromagnetic (EM) waves, in order to present a particular functionality. In this regard, nonlinear metasurfaces may present particular functionalities that remain to be discovered. In this paper, we numerically investigate the dynamic behaviors caused by the motion of charge carriers under the intense EM field at the gap of a single nonlinear split-ring resonator (NSRR) in the terahertz (THz) frequency range. We derive the mathematical model that is used to examine the excitation properties of the NSRR and then demonstrate various tuning regions. Analysis of the two-dimensional parameter space reveals that the NSRR exhibits periodic, chaotic patterns as the amplitude of the excitation field and the loss parameter vary. However, this chaotic behavior disappears when the loss parameter is very large. The period doubling that confirms the transition between the periodic and chaotic modes is explored using the bifurcation diagram. The sensitivity of the initial conditions is examined on three dynamic region plots. Our results correctly demonstrate that the NSRR exhibits the attractive phenomenon of multistability. The coexistence of two stable states is studied and confirmed on the basin of attractions for a fixed set of amplitude or loss parameters. The energy balance of the proposed model is well analyzed on the dynamic states and parameters to characterize the different oscillation regimes. The study of the multistability in the work represents an important first step toward the development of photonic memory devices in the THz frequency range.

Real-Time Megapixel Electro-Optical Imaging of THz Beams with Probe Power Normalization.

In this work, we present a simple method to improve the spatial uniformity of two-dimensional electro-optical imaging of terahertz (THz) beams. In this system, near-field THz images are captured by fully illuminating a sample using conventional optical microscope objectives. Unfortunately, due to the linear relationship between the optical probe power and the measured THz electric field, any spatial variation in probe intensity translates directly into a variation of the recorded THz electric field. Using a single normalized background frame information map as a calibration tool prior to recording a sequence of THz images, we show a full recovery of a two-dimensional flat field for various combinations of magnification factors. Our results suggest that the implementation of dynamic intensity profile correction is a promising avenue for real-time electro-optical imaging of THz beams.

Terahertz time-domain derivative spectrometer using a large-aperture piezoelectric micromachined device.

The engineering of optomechanical systems has exploded over the past decades, with many geometries and applications arising from the coupling of light with mechanical motion. The modulation of electromagnetic radiation in the terahertz (THz) frequency range through optomechanical systems is no exception to this research effort. However, some fundamental modulation capabilities for THz communications and/or high-speed data processing applications are yet to be established. Here, we demonstrate a THz time-domain derivative spectrometer based on a piezoelectric micromachined (PM) device. Insertion of the PM device into the THz beam path provides reference modulation for the lock-in detection unit, which in turn provides access to the nth-order derivative information of the incoming THz signal. Strikingly, the integration of the recorded derived signal leads to a recovered reference signal with an equivalent or even better signal-to-noise ratio, opening the door to a new type of highly sensitive THz measurements in the time domain.

Stokes-Mueller method for comprehensive characterization of coherent terahertz waves.

Ideally, the full characterization of coherent terahertz (THz) pulses would provide information on the amplitude and direction of its THz electric field, in space and in time, with unlimited dynamic range. Here, we propose and demonstrate a new approach based on the Stokes-Mueller formalism. Our approach can measure the full temporal and spatial variation of coherent THz fields, as well as its polarization state with a high dynamic range. This method employs a simple configuration, using a polarization state analyzer after the electro-optic sampling crystal. This technique could allow high sensitivity due to its ability to use thick detection crystals, which also would lead to improved spectral resolution by allowing longer scans in the time domain.

Contactless In Situ Electrical Characterization Method of Printed Electronic Devices with Terahertz Spectroscopy.

Printed electronic devices are attracting significant interest due to their versatility and low cost; however, quality control during manufacturing is a significant challenge, preventing the widespread adoption of this promising technology. We show that terahertz (THz) radiation can be used for the in situ inspection of printed electronic devices, as confirmed through a comparison with conventional electrical conductivity methods. Our in situ method consists of printing a simple test pattern exhibiting a distinct signature in the THz range that enables the precise characterization of the static electrical conductivities of the printed ink. We demonstrate that contactless dual-wavelength THz spectroscopy analysis, which requires only a single THz measurement, is more precise and repeatable than the conventional four-point probe conductivity measurement method. Our results open the door to a simple strategy for performing contactless quality control in real time of printed electronic devices at any stage of its production line.

Terahertz microscopy assisted by semiconductor nonlinearities.

Terahertz (THz) imaging is currently based on linear effects, but there is great interest on how nonlinear effects induced by terahertz radiation could be exploited to provide extra information that is unobtainable by conventional imaging schemes. In particular, at field strengths on the order of 100 kV cm-1 to 1 MV cm-1, transmission properties inside semiconductor materials are largely affected at the picosecond time-scale, which raise the prospect of interesting nonlinear imaging applications at THz frequencies. Here, we experimentally investigate a method to map the two-dimensional nonlinear near-field distribution of an intense THz pulse passing through a thin film-doped semiconductor. By inserting a metamaterial structure between the electro-optic sensor and the doped film, the nonlinear near-field dynamics shows a different and enhanced contrast of the sample when compared to its linear counterpart.

Adaptive spatiotemporal optical pulse front tilt using a digital micromirror device and its terahertz application.

We report a new method to temporally and spatially manipulate the pulse front tilt (PFT) intensity profile of an ultrashort optical pulse using a commercial microelectromechanical system, also known as a digital micromirror device (DMD). For our demonstration, we show terahertz generation in a lithium niobate crystal using the PFT pumping scheme derived from a DMD chip. The adaptive functionality of the DMD could be a convenient alternative to the more conventional grating required to generate a laser beam with a PFT intensity profile that is typically used for efficient optical rectification in noncollinear phase-matching conditions. In contrast to a grating, PFT using DMD does not suffer from wavelength dispersion, and exhibits overlap properties between grating and a stair-step echelon mirror.

Dynamics of spatiotemporal line defects and chaos control in complex excitable systems.

Spatiotemporal pattern formation governs dynamics and functions in various biological systems. In the heart, excitable waves can form complex oscillatory and chaotic patterns even at an abnormally higher frequency than normal heart beats, which increase the risk of fatal heart conditions by inhibiting normal blood circulation. Previous studies suggested that line defects (nodal lines) play a critical role in stabilizing those undesirable patterns. However, it remains unknown if the line defects are static or dynamically changing structures in heart tissue. Through in vitro experiments of heart tissue observation, we reveal the spatiotemporal dynamics of line defects in rotating spiral waves. We combined a novel signaling over-sampling technique with a multi-dimensional Fourier analysis, showing that line defects can translate, merge, collapse and form stable singularities with even and odd parity while maintaining a stable oscillation of the spiral wave in the tissue. These findings provide insights into a broad class of complex periodic systems, with particular impact to the control and understanding of heart diseases.

Is functional mobility an independent mortality risk factor in subjects with dementia?

OBJECTIVE: To investigate whether functional mobility is a predictor of 12-month mortality in elderly subjects with dementia. STUDY DESIGN: Prospective multicentre study performed in nine French university hospitals. Patients aged 75 years or more and hospitalised in medical wards via the emergency department were eligible. Those with a diagnosis of dementia were considered in the analyses. MAIN OUTCOME MEASURES: Patients' characteristics obtained through comprehensive geriatric assessment performed during the first week of hospitalisation. Functional mobility was assessed using the timed "Up & Go" test. The main outcome was time to death within the 12 months of follow-up. Bivariable relationships between each risk factor and mortality were assessed using a Cox regression model with one explanatory variable. For multivariable analysis, the Cox regression model was used in a stepwise method after examining potential confounders and interactions. RESULTS: In all, 589 patients had a diagnosis of dementia, and were considered in the present analyses. Their mean age was 86±6years and most (69%) were female. The prevalence of functional mobility disorders was 86%. After 12 months, 232 (39%) had died. After adjustment for potential confounders, functional mobility was associated with a significantly higher risk of 12-month mortality (HR=1.66; 95% CI=1.02-2.71; p=0.04). CONCLUSIONS: Impaired functional mobility as assessed by the timed Up & Go test identifies subjects with dementia at risk of unfavourable outcome.

Improving time and space resolution in electro-optic sampling for near-field terahertz imaging.

In this Letter, we present a significant improvement to time and space resolutions in electro-optic sampling (EO) for two-dimensional terahertz (THz) near-field imaging. Using a THz microscope, we readapt a recent EO sampling scheme based on optical probe spectrum filtering. Combined with an ultra-thin EO crystal, we achieve record broadband video-rate THz near-field imaging. Particularly, this new scheme improves the THz bandwidth, the imaging contrast, and the spatial resolution. To validate our method, we show THz near-field images ranging from 100 GHz to 4 THz with a spatial resolution up to λ/600 at 100 GHz. This demonstration positively affects the detection of intense THz pulses derived from the tilted-pulse-front excitation of lithium niobate and will accelerate our understanding of the interaction processes between electromagnetic waves and the conducting electrons of metallic interfaces.

[External validation of the short emergency geriatric assessment (SEGA) instrument on the SAFES cohort]. / Validation externe de la grille de fragilité SEGA sur la cohorte SAFES.

The aim of the study was to achieve the external validation of the SAGA instrument on the SAFES cohort. This was a prospective longitudinal multicentre cohort study, including patients aged 75 years or over, hospitalized in a short stay medical ward via emergency department. A comprehensive geriatric assessment was implemented. The psychometric validation enabled the study of feasibility, internal consistency, convergent, discriminant, and predictive validity of the instrument. The 1 306 patients of the cohort was 85±6 years, with a majority of women (65%). The completion rate of the SEGA instrument was 94%. Internal consistency was good (Cronbach alpha coefficient=0.7). Convergent validity was poor: Donini instrument (kappa=0.18; IC 95%=0.13-0.23), Rockwood instrument (kappa=0.04; IC 95%=0.02-0.06), and Winograd instrument (kappa=0.04; IC 95%=0.01-0.07). The ability of the instrument to discriminate clinically different groups was good. The SEGA instrument predicted well one-year mortality as well as one-year institution admission. Despite poor convergent validity (which is classic with frailty tools, SEGA instrument has satisfactory metrological properties, allowing its use in emergency departments and immediate post-emergency circumstances.

Dynamic creation of a light-induced terahertz guided-wave resonator.

We demonstrate a dynamic light-induced resonator for terahertz (THz) frequency light created on ultrashort time scales inside a planar waveguide. The resonator is created by patterned femtosecond photoexcitation of a one-dimensional array of photoconductive regions inside a silicon-filled parallel plate waveguide. The metal-dielectric photonic crystal is created on a 2 ps time scale, ten times faster than the 20 ps transit time of the THz light through the array. The resonance reveals itself through narrowband THz transmission enhancement with accompanying phase modulation producing an induced group delay of up to 10.8 ps near resonance.

Evaluation of a new geriatric foot versus the Solid Ankle Cushion Heel foot for low-activity amputees.

BACKGROUND: It is always a challenge to rehabilitate geriatric amputees to perform self-care skills at home with limited ambulation. A new geriatric foot (with a lower effective foot length) has been specifically designed to reduce residual limb stress and to ease the step completion. OBJECTIVES: The aim of this study is to evaluate the benefit of a new geriatric foot versus a Solid Ankle Cushion Heel foot for low-activity persons with transtibial amputation. STUDY DESIGN: Crossover study. METHODS: A total of 12 patients were included in this study. OUTCOME MEASURES: 2-min walking test, Quebec User Evaluation of Satisfaction with Assistive Technology 2.0 questionnaire and pressure socket measurements. RESULTS: The geriatric foot allows for greater patient satisfaction. The maximal pressure was significantly lower in the proximal anterior stump area. No statistical differences were obtained from the 2-min walking test. CONCLUSION: A geriatric foot designed with a low effective foot length improves the satisfaction and reduces proximal anterior socket pressures for poor-performing persons with transtibial amputation. CLINICAL RELEVANCE: The development and evaluation of feet specifically designed for geriatric persons with transtibial amputation could improve their specific requirements and satisfaction.

Regional distribution of mercury in sediments of the main rivers of French Guiana (Amazonian basin).

Use of mercury (Hg) for gold-mining in French Guiana (up until 2006) as well as the presence of naturally high background levels in soils, has led to locally high concentrations in soils and sediments. The present study maps the levels of Hg concentrations in river sediments from five main rivers of French Guiana (Approuague River, Comté River, Mana River, Maroni River and Oyapock River) and their tributaries, covering more than 5 450 km of river with 1 211 sampling points. The maximum geological background Hg concentration, estimated from 241 non-gold-mined streams across French Guiana was 150 ng g(-1). Significant differences were measured between the five main rivers as well as between all gold-mining and pristine areas, giving representative data of the Hg increase due to past gold-mining activities. These results give a unique large scale vision of Hg contamination in river sediments of French Guiana and provide fundamental data on Hg distribution in pristine and gold-mined areas.

[Quality of life in dementia: state of the knowledge]. / Qualité de vie et démence : état des connaissances.

BACKGROUND: Dementia is a chronic and evolutive disease, for which no curative treatment exists. Evaluating the quality of life of patients suffering from dementia is therefore an important component of management. AIMS: To summarise existing literature regarding quality of life instruments specific to dementia, and to identify factors associated with quality of life. METHODS: We analysed studies published between November 1996 and December 2010 and referenced in PubMed, and focusing on the development and/or validation of quality of life instruments specific to dementia, or studies having used any such instrument to evaluate a therapeutic intervention. RESULTS: Nine quality of life instruments were identified. Place of residence and level of education do not appear to play any significant role. Results were conflicting for age and sex. There appears to be a relation, albeit a weak one, with cognitive function. The factors most frequently associated with lower quality of life were behavioural disorders, dependence, and caregiver burden. Quality of life of patients under pharmacological treatment is poorly documented, while occupational therapy and cognitive stimulation appear to have moderate positive effects.

Ultrafast carrier dynamics in graphene under a high electric field.

We investigated ultrafast carrier dynamics in graphene with near-infrared transient absorption measurement after intense half-cycle terahertz pulse excitation. The terahertz electric field efficiently drives the carriers, inducing large transparency in the near-infrared region. Theoretical calculations using the Boltzmann transport equation quantitatively reproduce the experimental findings. This good agreement suggests that the intense terahertz field should promote a remarkable impact ionization process and increase the carrier density.

Factors associated with caregivers' underestimation of quality of life in patients with Alzheimer's disease.

OBJECTIVE: The aim of this study was to identify the factors associated with differences between how Alzheimer's disease (AD) patients and their caregivers rate the patient's health-related quality of life (QoL). METHODS: Cross-sectional, multicentre study. Patients were 65 years or more, suffering from mild to moderate AD, native French speakers, with a main caregiver. Interrater agreement of the QoL-AD was assessed using the intraclass coefficient. A generalised linear model was used to identify factors related to the difference in health-related QoL scores between patients and their caregivers. RESULTS: The 122 patients of the study were 82 ± 6 years old and mainly women (69%). Independent factors related to the difference between patients and caregivers were: Mini Mental State Exam score (ß = 0.32; 95% CI = 0.05-0.59); instrumental activities of daily living score (ß = -0.61; 95% CI = -1.14 to -0.07); total Neuropsychiatric Inventory score (ß = 0.10; 95% CI = 0.05-0.59), and Zarit's burden score (ß = 0.09; 95% CI = 0.01-0.17). CONCLUSION: Practitioners must take into account the trend towards underestimation when health-related QoL is rated by caregivers or proxies.

Nursing home admission in elderly subjects with dementia: predictive factors and future challenges.

OBJECTIVES: The aim of this study was to identify factors predictive of nursing home admission (NHA) over a period of 1 year among elderly subjects with dementia. METHODS: The study population was drawn from the SAFES cohort that was formed within a national research program into the recruitment of emergency departments in 9 teaching hospitals. Subjects were to have been hospitalized in a medical ward in the same hospital as the emergency department to which they were initially admitted. Subjects who experienced NHA before emergency department admission were excluded. Those with a confirmed diagnosis of dementia were considered in the present analysis. NHA has been defined as the incident admission into either a nursing home or other long term care facility within the follow-up period. Data obtained from a Comprehensive Geriatric Assessment were used in a Cox model to predict 1-year NHA. RESULTS: The 425 subjects of the study were 86 ± 6 years old, and were mainly women (63%). NHA rate was 40% (n = 172). Four factors were identified to increase NHA risk: age 85 or older (hazard ratio [HR] = 1.5; 95% confidence interval [CI] = 1.1-2.1), inability to use the toilet (HR = 2.5; 95% CI = 1.5-4.2), balance disorders (HR = 1.5; 95% CI = 1.1-2.1), and living alone (HR = 1.5; 95% CI = 1.1-2.1). Three factors decreased this risk significantly: inability to transfer (HR = 0.5; 95% CI = 0.3-0.8), increased number of children (HR = 0.88; 95% CI = 0.96-0.99), and increased initial Mini-Mental State Examination score (HR = 0.97; 95% CI = 0.8-0.9). CONCLUSION: NHA determinants in dementia are strongly linked to the patient's own characteristics but also to his or her physical or social environment. Interventions should target both members of the dyad "patient-caregiver" because both are affected by the disease.

Is health-related quality of life an independent prognostic factor for 12-month mortality and nursing home placement among elderly patients hospitalized via the emergency department?

OBJECTIVES: To assess whether health-related quality of life is an independent prognostic factor for mortality or nursing home placement in frail elderly patients. DESIGN: A prospective, multicenter study with a 12-month follow-up. SETTING: Nine French hospitals. PARTICIPANTS: A total of 1306 patients aged 75 and older hospitalized through an emergency department. MEASUREMENTS: Data obtained from sociodemographic characteristics, Comprehensive Geriatric Assessment and the Duke Health Profile (DHP) were used into a Cox model to identify prognostic variables for 12-month mortality and institutionalization. RESULTS: Crude mortality and nursing home placement rates were 34.1% (n = 445) and 16.1% (n = 210), respectively. Independent prognostic factors identified for mortality were: Comorbidity level (moderate: hazard ratio [HR] [95% confidence interval (CI)] = 1.40 [1.09-1.78]; severe: 2.70 [1.63-4.46]), dependence for activities of daily living (1.68 [1.06-2.67]), pressure sore risk (1.49 [1.16-1.90]), risk of malnutrition (2.09 [1.46-3.00]), delirium (2.25 [1.75-2.90]), and 10-point increase in the DHP perceived health score (0.96 [0.93-0.99]). Independent prognostic factors identified for nursing home placement were the following: living alone at home (1.82 [1.30-2.55]), having 2 children or more (0.71 [0.51-0.99]), dependence for activities of daily living (2.48 [1.39-4.44]), dementia (1.93 [1.39-2.69]), unplanned hospital readmission during follow-up (2.05 [1.45-2.91]), and 10-point increase in the DHP social health score (0.90 [0.83-0.99]). Balance troubles and risk of malnutrition were no more significant when adjusted for the DHP scores and other clinical variables. CONCLUSION: The perceived health and social health scores of the DHP were independent prognostic factors of survival and nursing home placement among hospitalized elderly patients, respectively. When associated with Comprehensive Geriatric Assessment, they could help screen frail patients to set up as early as possible targeted interventions to restore/maintain modifiable prognostic factors, such as nutritional status, functional ability, and social support.

[Frailty in older population: a brief position paper from the French society of geriatrics and gerontology]. / La fragilité de la personne âgée: un consensus bref de la Société française de gériatrie et gérontologie.

Frailty in the older population is a clinical syndrome which evaluate a risk level. The Frailty syndrome defines a reduction of the adaptation capacity to a stress. It can be modulated by physical, psychological and social factors. The screening of the frailty syndrome is relevant for older people without disability for basic activities of daily living. The clinical criteria of frailty must be predictive of the risk of functional decline and adverse outcomes, consensual at the international level, and easy to perform in primary care as well as in the clinical researches.