Search results for " sensor"

Fabrication of chirped fiber Bragg gratings by simple combination of stretching movements

2008

Abstract A new stretching technique to fabricate chirped fiber Bragg gratings using a nonchirped phase mask is presented. It is based on continuous stretching and continuous UV beam scanning, which ensures phase matching between periods along the grating. Simple combinations of the fiber stretching movements of a pair of piezoelectric transducers are used to avoid unwanted period blurring and wavelength shifting. A third piezoelectric transducer can be easily added to the system to provide independent apodization through phase mask dithering. Successful fabrication of apodized and nonapodized chirped fiber gratings has been performed with this technique.

Actively Q-switched all-fiber lasers

2007

Q-switching of fiber lasers using bulk elements has important drawbacks as reduced mechanical stability and high insertion losses. The development of efficient all-fiber modulation techniques is the key to obtain robust, compact and efficient Q-switched all-fiber lasers. Certainly, the development of fiber Bragg gratings (FBG) has been crucial to make progress on fiber lasers. FBGs permit a simple way to assemble all-fiber laser cavities and can be written in the active fiber itself. The Q-factor of this type of cavities is determined by the reflectivity of the FBGs and the losses of the fiber. Here, we focus on the use of magnetostrictive materials and the acousto-optic interaction to deve…

Radiation Vulnerability of Fiber Bragg Gratings in Harsh Environments

2015

International audience; The difficulties encountered in the implementation of a temperature or strain sensor based on fiber Bragg grating (FBG) in a harsh radiative environment are introduced. We present the choices made to select both a radiation-resistant fiber in terms of transmission and also the grating inscription conditions necessary to write radiation tolerant FBGs in such fibers with a femtosecond laser. The radiation response of these gratings was also studied under radiation at dose up to 1 MGy. The comparison between Ge-free and Ge-doped fibers was highlighted.

Decentralized Lightweight Group Key Management for Dynamic Access Control in IoT Environments

2020

Rapid growth of Internet of Things (IoT) devices dealing with sensitive data has led to the emergence of new access control technologies in order to maintain this data safe from unauthorized use. In particular, a dynamic IoT environment, characterized by a high signaling overhead caused by subscribers' mobility, presents a significant concern to ensure secure data distribution to legitimate subscribers. Hence, for such dynamic environments, group key management (GKM) represents the fundamental mechanism for managing the dissemination of keys for access control and secure data distribution. However, existing access control schemes based on GKM and dedicated to IoT are mainly based on ce…

Pain elicited by blunt pressure: neurobiological basis and clinical relevance.

2002

An Embedded Biometric Sensor for Ubiquitous Authentication

2013

Communication networks and distributed technologies move people towards the era of ubiquitous computing. An ubiquitous environment needs many authentication sensors for users recognition, in order to provide a secure infrastructure for both user access to resources and services and information management. Today the security requirements must ensure secure and trusted user information to protect sensitive data resource access and they could be used for user traceability inside the platform. Conventional authentication systems, based on username and password, are in crisis since they are not able to guarantee a suitable security level for several applications. Biometric authentication systems…

Assessment of the fundamental flexural guided wave in cortical bone by an ultrasonic axial-transmission array transducer

2013

Abstract The fundamental flexural guided wave (FFGW), as modeled, for example, by the A0 Lamb mode, is a clinically useful indicator of cortical bone thickness. In the work described in this article, we tested so-called multiridge-based analysis, based on the crazy climber algorithm and short-time Fourier transform, for assessment of the FFGW component recorded by a clinical array transducer featuring a limited number of elements. Methods included numerical finite-element simulations and experiments in bone phantoms and human radius specimens ( n  = 41). The proposed approach enabled extraction of the FFGW component and determination of its group velocity. This group velocity was in good ag…

Neuropathologic and morphometric studies in hereditary motor and sensory neuropathy type II with neurofilament accumulation.

1986

Histological, electron microscopic and morphometric data on sural nerve, muscle, and skin biopsies of three patients affected by autosomal dominant hereditary motor and sensory neuropathy type II with neurofilament accumulation, whose neurological, cardiological and electrophysiological data have been provided in a previous paper disclosed focally enlarged myelinated axons, due to aggregation of neurofilaments in sural nerves of all 3 biopsied patients, as well as densely packed clusters of filaments in occasional non-myelinated axons without axonal enlargement, in several fibroblasts and endothelial cells in muscle and particularly in skin. This accumulation of filaments was less pronounce…

Ultrasonic demonstration of small pancreatic islet cell tumors.

1982

In three patients real-time sonography successfully localized small pancreatic islet cell tumors measuring 7, 8, and 17 mm in size. Ultrasound is suggested as the initial radiologic examination for localization of endocrine pancreatic tumors. If ultrasound is negative or equivocal, computerized tomography, arteriography, and pancreatic venous sampling are indicated.

Montessori praktiskās dzīves un sensorikas materiālu izmantošana 3-4 gadus vecu bērnu patstāvības attīstībā

2018

Darba mērķis ir popularizēt Marijas Montessori izstrādātos mācību materiālus un pedagoģiskos pamatprincipus saistībā ar mūsdienu straujo dzīves ritmu un jaunās pirmsskolas izglītības vadlīniju ieviešanu. Darbā izceltas nozīmīgākās īpašības un prasmes, kuras ir par pamatu patstāvīgas personas veidošanā, un to attīstības veicināšanas iespējas. Darbā pētīts kā M. Montessori veidotie praktiskās dzīves un sensoriskas materiāli veicina šo īpašību un prasmju attīstību 3-4 gadus veciem bērniem; kā šie materiāli ar savu specifisko uzbūvi atbilst pētnieku atziņām par mācību procesa efektivitātes veicināšanu. Darbā apskatīta arī vides un pedagoga nozīmība un šo trīs faktoru mijiedarbība. Pētījuma salī…