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.

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.

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.

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.

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.

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.

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.

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.

Predictors of rapid cognitive decline among demented subjects aged 75 or more: ('Sujet Agé Fragile--Evaluation et Suivi' Cohort-SAFES).

OBJECTIVE: To identify factors predictive of rapid cognitive decline (RCD) among elderly subjects aged 75 or over suffering from dementia. METHODS: The analysis concerned 250 patients drawn from the 'Sujet Agé Fragile--Evaluation et Suivi' (SAFES) cohort, presenting a dementia syndrome at inclusion and followed-up for at least 1 year. RCD was defined as the loss of at least 3 points on the Mini-Mental State Examination (MMSE) in the follow-up period of 12 months. All patients underwent a standardised geriatric evaluation. Logistic regression was used to identify factors predictive of RCD. RESULTS: In the study sample, 84 patients (33.6%) presented RCD. The factors identified in multivariate analysis as predictive of RCD were: high level of education (OR = 7.8, 95% CI = [1.9-31.2], p = 0.004), risk of depression (OR = 1.8, 95% CI = [1.02-3.18], p = 0.048, and the initial MMSE score (OR = 1.1, 95% CI = [1.0-1.2], p = 0.002). Among subjects with a main caregiver (n = 177), the predictive factors were malnutrition or risk thereof (OR = 4.2, 95% CI = [1.3-14.1], p = 0.02), risk of a fall (OR = 2.6, 95% CI = [1.1-6.1], p = 0.03, caregiver burden (OR = 2.6, 95% CI = [1.1-6.4], p = 0.04) and initial MMSE score (OR = 1.1, 95% CI = [1.0-1.3], p = 0.004). CONCLUSIONS: As soon as dementia is diagnosed in elderly subjects, information should be collected about the subject's socioeconomic status, nutritional status, risk of falling, mood state, and caregiver burden. This would enable the provision of appropriate therapeutic care, and make it possible to adapt follow-up in case of a risk of accelerated cognitive deterioration.

Transcultural adaptation and psychometric validation of a French-language version of the QoL-AD.

OBJECTIVES: The aim of this study was to assess the psychometric properties and the transcultural adaptation into French of the quality-of-life in Alzheimer's disease (QoL-AD). METHODS: A total of 120 patient-proxy pairs were recruited in six French hospitals and one French-speaking Swiss hospital to take part in the study. The patients presented mild to moderate AD (MMSE > or = 10). The QoL-AD was administered by an interviewer for patients and was self-administered for caregiver proxies. Thus, the psychometric validation enabled the study of feasibility, acceptability, reliability and convergent and discriminant validity of the instrument. RESULTS: The French version of the QoL-AD showed good internal consistency (Cronbach's alpha coefficient > or = 0.70) and good reliability (Intra-class correlation > 0.80) at a 2-week interval, for patient and caregiver questionnaires. Convergent validity, as indicated by correlation between the QoL-AD (disease-specific instrument) and the dimensions of the Duke Health Profile (generic instrument), was also good for eight dimensions in the Duke profile (p < 0.05). Discriminant validity showed a significant difference for depression (p = 0.0025) and did not show significant difference for two groups of dementia (p = 0.11). CONCLUSION: There is now a validated French version of the QoL-AD available, following transcultural adaptation according to international recommendations, which possesses good psychometric qualities.

Development of an individualized service plan tool and rules for case management in Québec.

From past experience with integrated service delivery, there appears to be a need for a clinical tool to help case managers plan, monitor, and coordinate services. In this context the Québec Ministry of Health and Social Services created a task force to suggest improvements to the Individualized Service Plan tool included in the Multiclientele Assessment Tool. This article reports the findings of this multidisciplinary task force working with various clienteles (older, with physical or mental disabilities, mental diseases). Based on a literature review and recent results from the Program of Research on the Integration of Services for the Maintenance of Autonomy, the task force proposed a dynamic, concise, user-friendly tool and a clear definition of how it should be used. The Individualized Service Plan must list the patient's needs, with an orientation regarding the action plan for each, and a list of services allocated in response to these needs that work in the defined direction. The tool must also contain a section for analyzing variations between the services needed and allocated. This tool was presented to case managers for validation and received an enthusiastic response. It should be implemented in the coming years in the provincial Multiclientele Assessment Tool.

Normal and pathological aging of attention in presymptomatic Huntington's, Huntington's and Alzheimer's Disease, and nondemented elderly subjects.

BACKGROUND: Attention models view attention as having at least two components: endogenous attention defined as executive and directed by voluntary acts, and exogenous attention defined as automatic and directed by external stimulation. METHODS: Three studies (2 of our own) were designed to evaluate the decline of these two components of attention in normal aging and two neurodegenerative diseases. Standardized tests derived from Posner's model of visuospatial attention were administered to normal healthy elderly participants (n = 13), patients suffering from Huntington's disease (HD; n = 17) and Alzheimer's disease (n = 15), and matched control subjects (n = 57). Outcome measures were reaction time (RT) and RT difference score (defined as invalid RT minus valid RT). RESULTS: In healthy elderly participants, the decline was more pronounced for endogenous attention in situations of perceptual conflict. In Alzheimer's disease, there was a significant decline in both attention components, while in HD, voluntary attention was markedly impaired and automatic attention preserved. CONCLUSIONS: Normal aging and HD are characterized by decreased endogenous attention in situations of perceptual conflict. Our data support previous findings that older people display impairment of attention in complex perceptual situations. We propose a model which allows for the separation of attention pathologies, thus improving therapeutic strategies for patients and elderly.

Potentially inappropriate use of psychotropic medications in hospitalized elderly patients in France: cross-sectional analysis of the prospective, multicentre SAFEs cohort.

BACKGROUND: In France, there is evidence to suggest that 50% of elderly individuals are prescribed psychotropic medications. However, it is known that use of these agents increases the risk of falls, fractures and delirium in older people. OBJECTIVE: To study the consumption of 'potentially inappropriate medication' (PIM) among patients aged>or=75 years, paying particular attention to psychotropic drugs and the factors influencing the use of 'potentially inappropriate psychotropics' (PIPs). METHOD: This was a cross-sectional analysis of a prospective multicentre cohort of 1306 hospitalized French patients aged>or=75 years (the SAFEs [Sujet Agé Fragile: Evaluation et suivi (Frail Elderly Subjects: Evaluation and follow-up)] cohort). The present analysis involved the 1176 patients for whom there was information on the usual treatments being taken in the 2 weeks before hospitalization. The drugs were coded according to the Anatomical Therapeutic Chemical classification; the Beers list as updated in 2003 defined which medications were considered PIPs. Standardized geriatric assessment variables were recorded on inclusion in the study. Logistic regression analysis was performed to identify factors linked to use of psychotropics and PIPs. RESULTS: The mean number of drugs taken was 5.7+/-2.9 per patient. Twenty-eight percent of patients took at least one PIM. The number of patients who had taken at least one psychotropic drug in the 2 weeks before hospitalization (mean 1.6+/-0.9 psychotropics per patient) was 589 (50.1%). More than half of both the 510 patients with a depressive syndrome and the 543 patients affected by dementia were treated with psychotropics. Multivariate analysis showed that prescription of psychotropics was linked to the presence of a dementia syndrome (odds ratio [OR]=1.4; 95% CI 1.1, 1.9; p=0.03), the presence of a depressive syndrome (OR=1.7; 95% CI 1.3, 2.1; p<0.001), living in an institution (OR=2.2; 95% CI 1.5, 3.4; p<0.001), use of more than five drugs (OR=3.2; 95% CI 2.5, 4.2; p<0.001) and Charlson's co-morbidity score>1 (OR=0.6; 95% CI 0.5, 0.8; p=0.001). Nineteen percent of all psychotropics prescribed were PIPs. Of these PIPs, 66.5% were anxiolytics, 28.4% were antidepressants and 5.1% were antipsychotics. Use of PIPs in the multivariate analysis was associated only with consumption of more than five drugs (OR=1.7; 95% CI 1.1, 2.5; p=0.01). CONCLUSION: PIM use is common among hospitalized older adults in France. The most important determinant of risk of receiving a psychotropic medication or a PIP was the number of drugs being taken. The elderly, who have multiple co-morbidities, complex chronic conditions and are usually receiving polypharmacy, are at increased risk for adverse drug events. These adverse events are often linked to problems that could be preventable such as delirium, depression and falls. Regular review of prescriptions would help optimize prescription of psychotropics in the elderly. The Beers list is a good tool for evaluating PIMs but is too restrictive with respect to psychotropics; in the latter respect, the list could usefully be widened.

Incidence and main factors associated with early unplanned hospital readmission among French medical inpatients aged 75 and over admitted through emergency units.

BACKGROUND: among elderly patients, readmission in the month following hospital discharge is a frequent occurrence which involves a risk of functional decline, particularly among frail subjects. While previous studies have identified risk factors of early readmission, geriatric syndromes, as markers of frailty have not been assessed as potential predictors. OBJECTIVE: to evaluate the risk of early unplanned readmission, and to identify predictors in inpatients aged 75 and over, admitted to medical wards through emergency departments. DESIGN: prospective multi-centre study. SETTING: nine French hospitals. SUBJECTS: one thousand three hundred and six medical inpatients, aged 75 and older admitted through emergency departments (SAFES cohort). METHODS: using logistic regressions, factors associated with early unplanned re-hospitalisation (defined as first unplanned readmission in the thirty days after discharge) were identified using data from the first week of hospital index stay obtained by comprehensive geriatric assessment. RESULTS: data from a thousand out of 1,306 inpatients were analysed. Early unplanned readmission occurred in 14.2% of inpatients and was not related with sociodemographic characteristics, comorbidity burden or cognitive impairment. Pressure sores (OR = 2.05, 95% CI = 1.0-3.9), poor overall condition (OR = 2.01, 95% CI = 1.3-3.0), recent loss of ability for self-feeding (OR = 1.9, 95% CI = 1.2-2.9), prior hospitalisation during the last 3 months (OR = 1.6, 95% CI = 1.1-2.5) were found to be risk factors, while sight disorders appeared as negatively associated (OR = 0.5, 95% CI = 0.3--0.8). CONCLUSIONS: markers of frailty (poor overall condition, pressure sores, prior hospitalisation) or severe disability (for self-feeding) were the most important predictors of early readmission among elderly medical inpatients. Early identification could facilitate preventive strategies in risk group.

[Early indicators of prolonged hospitalization of the elderly: pilot study at Strasbourg University Hospital]. / Indicateurs précoces de durée de séjour prolongée chez les sujets âgés: étude pilote réalisée au CHRU de Strasbourg.

OBJECTIVES: The aim of this study was to identify early indicators of prolonged hospital stays by elderly patients. METHODS: This prospective pilot study, conducted at Strasbourg University Hospital, included patients aged 75 years or older who were hospitalized via the emergency department (SAFES cohort: Sujet Agé Fragile: Evaluation et suivi, that is, Frail Elderly Subjects: Evaluation and Follow-up). A gerontologic evaluation of these patients during the first week of their hospitalization furnished the data for an exact logistic regression. Two definitions were used for prolonged hospitalization: 30 days and a composite number adjusted for diagnosis-related group according to the French classification (f-DRG). RESULTS: The analysis examined 137 hospitalizations. More than two thirds of the patients were women (73%), with a mean age of 84 years. Twenty-four hospitalizations (17%) lasted more than 30 days, but only 6 (4%) lasted beyond the DRG-adjusted limit. No social or demographic variables appeared to affect the length of stay, regardless of the definition of prolonged stay. No indicator was associated with the 30-day limit, but clinical markers were linked to prolongation assessed by f-DRG adjustment. A "risk of malnutrition" (OR=14.07) and "mood disorders" (OR=2,5) were both early markers for prolonged hospitalization. Although not statistically significant, "walking difficulties" (OR=2.72) and "cognitive impairment" (OR=5.03) appeared to be associated with prolonged stays. No association was seen with either the variables measured by Katz's Activities of Daily Living Index or its course during hospitalization. CONCLUSION: Our study shows that when generally recognized indicators of frailty are taken into account, a set of simple items enables a predictive approach to the prolongation of emergency hospitalizations of the elderly.

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.