Multi-band OFDM UWB receiver with narrowband interference suppression

A multi band orthogonal frequency division multiplexing (MB-OFDM) compatible ultra wideband (UWB) receiver with narrowband interference (NBI) suppression capability is presented. The average transmit power of UWB system is limited to -41.3 dBm/MHz in order to not interfere existing narrowband systems. Moreover, it must operate even in the presence of unintentional radiation of FCC Class-B compatible devices. If this unintentional radiation resides in the UWB band, it can jam the communication. Since removing the interference in digital domain requires higher dynamic range of analog front-end than removing it in analog domain, a programmable analog notch filter is used to relax the receiver requirements in the presence of NBI. The baseband filter is placed before the variable gain amplifier (VGA) in order to reduce the signal swing at the VGA input. The frequency hopping period of MB-OFDM puts a lower limit on the settling time of the filter, which is inverse proportional to notch bandwidth. However, notch bandwidth should be low enough not to attenuate the adjacent OFDM tones. Since these requirements are contradictory, optimization is needed to maximize overall performance. Two different NBI suppression schemes are tested. In the first scheme, the notch filter is operating for all sub-bands. In the second scheme, the notch filter is turned on during the sub-band affected by NBI. Simulation results indicate that the UWB system with the first and the second suppression schemes can handle up to 6 dB and 14 dB more NBI power, respectively. The results of this work are not limited to MB-OFDM UWB system, and can be applied to other frequency hopping systems

TRANSLATION-FAVORABLE FLAT SURFACES IN 3-SPACES

In the paper, we obtain the complete classification of Translation-Factorable (TF-) surfaces with vanishing Gaussian curvature in Euclidean and Minkowski 3-space

Učinci obrade silanom na fizička i mehanička svojstva ploče iverice izrađene s ureaformaldehidnim ljepilom

In this study, the effect of silane on particleboard physical and mechanical properties was investigated. Silane was mixed in particleboards with two different methods. In the first method, silane was mixed with wood chips namely as a pretreatment of wood chips. In the second method, silane was mixed with urea-formaldehid adhesive. The amounts of silane used in both methods were 1 %, 2 % and 3 % of the particles based on the dry weight. Urea formaldehyde with 65 % solid content was used as adhesive. Ammonium sulfate (1 %) was added as a hardener to the used adhesive. The target density of three-layer particleboards manufactured was 550 kg/m3. The properties of particleboards evaluated include thickness swelling, bending properties and internal bond strength. Results indicate that particleboards thickness swelling values increase with the use of silane. Overall, pretreatment of the wood particles provided better mechanical properties than the addition of silane to the adhesive solution. Flexure strength and flexure modulus of particleboards were significantly improved by use of silane. Pretreatment of particles with 2 % silane yielded the best improvement of modulus of rupture and modulus of elasticity. For the particleboards prepared with pretreated wood chips with silane, the highest increase of the flexure modulus and flexure strength was 20 % and 40 %, respectively. Pretreatment of wood particles with 3 % of silane nearly doubled internal bond strength of the particleboards. Silane pretreatment can be an alternative method for the improvement of particleboard mechanical properties.U ovom je istraživanju ispitivan učinak silana na fizička i mehanička svojstva ploče iverice. Obrada ploče iverice silanom provedena je primjenom dviju metoda. U prvoj metodi silan je pomiješan s drvnim iverjem, što je ujedno bila predobrada drvnog iverja. U drugoj metodi silan je pomiješan s urea-formaldehidnim ljepilom. Količine silana upotrijebljenoga u obje metode bile su 1 %, 2 % i 3 % s obzirom na sadržaj suhe tvari. Kao ljepilo je rabljeno urea-formaldehidno ljepilo sa 65 % suhe tvari. Ljepilu je dodan amonijev sulfat (1 %) kao otvrdnjivač Ciljana gustoća proizvedene troslojne ploče iverice bila je 550 kg/m3. Istražena svojstva iverice obuhvatila su debljinsko bubrenje, savijanje i čvrstoću raslojavanja. Rezultati pokazuju da se pri upotrebi veće količine silana vrijednost debljinskog bubrenja ploče iverice povećava. Prethodna obrada drvnog iverja rezultirala je boljim mehaničkim svojstvima iverice nego dodavanje silana ljepilu. Čvrstoća na savijanje i modul savitljivosti ploče iverice znatno su poboljšani primjenom silana. Predobradom iverja s 2 % silana postignuto je najbolje poboljšanje modula loma i modula elastičnosti. Za ploču ivericu pripremljenu s drvnim iverjem prethodno obrađenim silanom najveće povećanje modula savitljivosti i čvrstoće na savijanje iznosilo je 20 %, odnosno 40 %. Predobrada drvnog iverja s 3 % silana gotovo je udvostručila čvrstoću raslojavanja iverice. Predobrada silanom može biti alternativna metoda za poboljšanje mehaničkih svojstava ploče iverice

Bishop Çatısı ile İlişkilendirilmiş Hasimoto Yüzeyleri

In this paper, we investigate the Hasimoto surfaces in Euclidean 3- space. Firstly,we investigate the geometric properties of these surfaces in Euclidean 3-space.Especially, we obtain the curvatures of Hasimoto surface according to Bishop frame.Then we give some characterization of parameter curves obtained according to Bishopframe of Hasimoto surfaces.Bu çalışmada Öklidyen 3-uzayındaki Hasimoto yüzeyleri incelenmiştir. İlk olarak, Öklidyen 3-uzayındaki Hasimoto yüzeylerinin geometrik özellikleri incelenmiştir. Özellikle Bishop çatısı ile ilişkilendirilmiş bu yüzeylerin eğrilikleri elde edilmiştir. Daha sonrasında bu yüzeylerin Bishop çatısına göre parametre eğrilerinin bazı karakterizasyonları verilmiştir

Biomechanical Effects of the Implant Designed for Posterior Dynamic Stabilization of the Lumbar Spine (L4-L5): A Finite Element Analysis Study

This study aims to design a new pedicle-screw-based posterior dynamic stabilization (DS) implant, which can help stabilize the spine normally, using the finite element (FE) method, and to determine and compare its biomechanical effects. Four different implant and device components that maintain the range of motion (ROM) within the standard limits were created with the SOLIDWORKS program, and the ABAQUS CAD simulation program and MATLAB program were used together to calculate the range of motion. In all devices, some rods connect L4-L5 vertebrae and are connected with screws, screws placed in the spines, and pins and nuts that complete the connection of the screws with the rod. Based on computed tomography scan data, robust and different implant-treated models of the lumbar spine were simulated under physiological loading conditions. For all designed devices, the range of motion was measured in axial rotation, lateral bending, and flexion-extension directions, and adjacent level effect and restoration percentages were calculated in all directions. With the iterations in the design of the implant parts, an acceptable 70% restoration percentage in the movement of the spine with the implant has been tried to be achieved in all directions. With the device whose optimum data were obtained, 58% for flexion, 70% for extension, 67%, and 52% for lateral bending and axial rotations, respectively, were achieved. It can be said that the pedicle-screw design realized with this study will be applicable after successful experimental validation and clinical trials

On surfaces endowed with a canonical principal direction in Euclidean 4-spaces

In this paper, we introduce canonical principal direction (CPD) submanifolds with higher codimension in Euclidean spaces. Then we obtain a classification of surfaces endowed with CPD relative to a fixed direction in Euclidean 4-space.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK)This paper is a part of the PhD thesis of the first author, who was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) as a PhD scholar. The authors would like to express their sincere gratitude to the referees for their valuable suggestions