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Sistem pengenalan pola berbasis biometri bertujuan untuk mendapatkan akurasi pengenalan yang baik. Dalam aplikasi nyata, umumnya sistem tersebut merupakan sistem unimodal yang memiliki beberapa kekurangan. Sistem multimodal dapat mengatasi kekurangan tersebut. Modalitas yang berbeda lebih sesuai untuk aplikasi yang berbeda. Penelitian sebelumnya menguji tingkat pengenalan citra pembuluh darah dengan menggunakan deskriptor ciri-lokal. Dalam paper ini dibandingkan performa teknik klasifikasi berbasis Linear Discriminant Analysis, yaitu Fast Null-space based Linear Discriminant Analysis (FNLDA) dan Direct Linear Discriminant Analysis (DLDA) untuk mengenali seseorang berdasarkan citra multimodal wajah atau pembuluh darah. Representasi citra wajah atau pembuluh darah hasil ekstraksi ciri digunakan untuk mendapatkan vektor ciri citra. Kemudian, data tersebut dicocokkan dan akurasi pengenalan dari teknik klasifikasi yang diuji dapat ditentukan. Dari hasil pengujian didapatkan performa teknik klasifikasi yang lebih baik untuk mengenali seseorang berdasarkan citra multimodal wajah atau pembuluh darah, ditinjau dari tingkat akurasi pengenalannya adalah FNLDA.

Introduction: In Africa, the first case of COVID-19 was reported in February 2020. Mauritania’s first case was confirmed in March 2020. Methodology: We provide an update of the COVID-19 epidemic in Mauritania as of December 2020, and describe the country’s Health System Response. Results: In total, 133,749 diagnostic tests were performed, 14,364 (10.7%) were positive (309 cases/100,000 inhabitants). Case fatality rate was 2.4%. The 20-39 year-olds (41%) and males (59.1%) were most commonly affected. Comorbidities among fatal cases included cardiovascular diseases (44.8%) and diabetes (37.1%). Clinical symptoms included fever (57%), cough (52%), running nose (47%) and headache (26%). After the first case, prevention measures were progressively tightened, and quarantine implemented for all suspected cases. Schools and universities were closed, and flights to Mauritania suspended. Restaurants and cafeterias were closed, and night curfews installed. Friday prayers were suspended nationwide, and movements between regions restricted. These measures helped to contain the spread of SARS-CoV-2 during the first pandemic wave, which peaked in June 2020 with low rates. However, the number of daily cases reached high levels in December 2020, during the second wave (40.1% of all cases and 48.9% of deaths). During the first wave, there were 38 ICU beds nationwide, but the ICU’s capacity increased in short time. Conclusions: Mauritania has passed through the first pandemic wave with relatively low case fatality rates, currently being at the end of the second wave. As the country’s health system is very vulnerable, there is a need for strict public health measures during epidemics.

A new outbreak of Rift Valley fever (RVF) occurred in Mauritania from September to November 2020, involving 78 reported human cases and 186 reported animal cases. Eleven out of the 13 regions of the country were affected by the epidemic, with the highest number of both human and animal cases in Tagant, Assaba and Brakna regions. The most affected animal species in this outbreak was camels, followed by small ruminants. Among the 10 mosquito species caught, 7 species, Culex poicilipes, Cx. quinquefasciatus, Cx. antennatus, Cx. univitattus, Aedes vexans, Mansonia africana and Ma. uniformis, are known to be involved in the transmission of RVF virus. Phylogenetic analyses based on the partial NSs gene revealed close proximity between the human/animal Mauritania 2020 viral strains and the Mauritania 2015/Niger 2016 strains, suggesting re-emergence of the RVF virus in the country since the last reported outbreak in 2015.

A method is developed to calculate the length into a sample to which a Frequency Domain Thermoreflectance (FDTR) measurement is sensitive. Sensing depth and sensing radius are defined as limiting cases for the spherically spreading FDTR measurement. A finite element model for FDTR measurements is developed in COMSOL multiphysics and used to calculate sensing depth and sensing radius for silicon and silicon dioxide samples for a variety of frequencies and laser spot sizes. The model is compared to experimental FDTR measurements. Design recommendations for sample thickness are made for experiments where semi-infinite sample depth is desirable. For measurements using a metal transducer layer, the recommended sample thickness is three thermal penetration depths, as calculated from the lowest measurement frequency.

A frequency-domain thermoreflectance (FDTR) system with a frequency range of 1 Hz to 75 MHz is presented. The wide bandwidth of pump modulation frequency enables enhanced simultaneous thermophysical property characterization of bulk and thin-film materials. The wide bandwidth FDTR system is demonstrated with simultaneous measurements of in-plane and cross-plane thermal conductivities of sapphire and muscovite mica, thickness and thermal conductivity of gold/titanium thin films, and isotropic thermal conductivity and volumetric heat capacity of lithium niobate and silicon. Thermophysical properties measured with FDTR are compared to literature values or independent measurements for verification. Finally, at low frequencies, a negligible error was achieved in the numerical integration of the heat diffusion equation with a Gauss-Legendre quadrature method solved with 400 integration points and an upper integration limit of 16weff, where weff is the effective pump-probe 1/e2 radius.

A predictive analytical model for the thermal conductivity of Aluminum/transition metal based high-entropy alloys based on contributions from the electron and lattice subsystems is presented. Lattice conductivity is modeled as an oscillator damped by electron-phonon and defect scattering. Electron subsystem conductivity is dominated by scattering from the aperiodic crystal potential arising from alloying atom induced lattice disorder; its effect was quantitatively calculated using a virtual crystal approximation. We show that model predictions agree with published values and for an exemplar high-entropy alloy largely based on transition (i.e., non-refractory) elements, AlxCoCrCuyFeNi. Within this alloy system, the crystal structure varies between face centered cubic and body centered cubic depending on composition and temperature, and it was found that thermal conductivity behaves as a weighted-average composite of the multiple phases.

High power semiconductor applications require a die attach material with high thermal conductivity to efficiently release the heat generated from these devices. Current die attach solutions such as eutectic solders and high thermal conductive silver epoxies and sintered silver adhesives have been industry standards, however may fall short in performance for high temperature or high stress applications. This presentation will focus on development of a reinforced, sintered silver die attach solution for high power semiconductor applications with focus on a pressure-less, low temperature sintering technology that offers high reliability for high temperature (250°C) applications. The electronic, optoelectronic, and semiconductor industries have the need for high performance adhesives, in particular, high power devices require low-stress, high thermal conductivity, thermally stable, and moisture resistant adhesives for the manufacture of high reliability devices. This paper introduces a new reinforced sintered silver adhesive based on the “resin-free” Conductive Fusion Technology. The high performance adhesive offers a robust solution for high temperature, high reliability applications. Conductive Fusion Technology consists of a high thermal conductivity silver component blended with a non-conductive, low-modulus powder component. The non-conductive powder component comprises an organically modified inorganic material that exhibits excellent thermal stability at temperatures exceeding 250°C. Properties of the sintered silver adhesive, such as storage modulus, can be modified by varying the content of the non-conductive component.

Studies of size effects on thermal conductivity typically necessitate the fabrication of a comprehensive film thickness series. In this Letter, we demonstrate how material fabricated in a wedged geometry can enable similar, yet higher-throughput measurements to accelerate experimental analysis. Frequency domain thermoreflectance (FDTR) is used to simultaneously determine the thermal conductivity and thickness of a wedged silicon film for thicknesses between 100 nm and 17 μm by considering these features as fitting parameters in a thermal model. FDTR-deduced thicknesses are compared to values obtained from cross-sectional scanning electron microscopy, and corresponding thermal conductivity measurements are compared against several thickness-dependent analytical models based upon solutions to the Boltzmann transport equation. Our results demonstrate how the insight gained from a series of thin films can be obtained via fabrication of a single sample.

High power semiconductor applications such as RF and microwave applications, GaN and SiC power devices and High Brightness LEDs (HBLED), require a die attach material with high thermal conductivity to efficiently release the heat generated from these devices. In these types of applications, the main path for heat dissipation is from the device through the die attach material. In order to provide an effective thermal path, it is important for the die attach material to maintain good interfacial contact with backside of the die and substrate. In addition to meeting the necessary thermal performance, die attach materials are required to offer high reliability, ready for high volume manufacturing (HVM), and be readily available while meeting RoHS compliance requirements. Current die attach solutions such as eutectic solders (e.g. AuSn and lead (Pb) solders) have been industry standards offering good reliability and effective thermal conductivity, however both have their drawbacks. High thermal conductive silver epoxies and sintered silver adhesives have provided an attractive alternative to solders, but may fall short in performance for high temperature or high stress applications. Recent developments in sintered silver die attach pastes offer the latest solutions to replacing solders in the semiconductor market, providing a RoHS compliant material with unmatched thermal performance and high reliability. This presentation will focus on development of a reinforced sintered silver die attach solution for high power semiconductor applications with focus on a pressure-less, low temperature sintering technology that offers high reliability for high temperature (250°C) applications.

Replacing fossil fuels with biomass-based alternatives is a potential carbon neutral, renewable and sustainable option for meeting the world’s growing energy demand. However, pyrolytic conversions of biomass-to-biofuels suffer marginal total energy gain, and technical limitations such as bio-oils’ high viscosity and oxygen contents that result in unstable, corrosive and low-value fuels. This work demonstrates a new integrated biorefinery process for the co-production of biofuels and silver nanomaterials. By impregnating pure cellulose and corn stalk with silver nitrate, followed by pyrolysis, the gas yield (especially hydrogen) increases substantially. The condensable bio-oil components of the impregnated samples are considerably higher in furfurals (including 5-hydroxymethylfurfural). Though the overall activation energy barrier, as determined via the Distributed Activation Energy Model, does not change significantly with the silver nitrate pre-treatment, the increase in gases devolatilized, and improved 5-hydroxymethylfurfural yield, suggest a catalytic effect, potentially increasing decarboxylation reactions. After using this metal impregnation to improve pyrolysis fuel yield, following pyrolysis, the silver-char composite materials are calcined to remove the biomass template to yield silver nanomaterials. While others have demonstrated the ability to biotemplate such nanosilver on cellulosic biomass, they consider only impregnation and oxidation of the template. This is the first work that demonstrates the potential to extract upgraded biorenewable fuels during the biotemplating of nanomaterials, the same nanomaterials often used in catalytic energy applications.

This paper presents a coordinated framework of prepared data packet transmission in a transmission session. Automated guide vehicles (AGVs) with an onboard 1-km range APC transmitter are used to establish the network environment for testing the prepared packet transmission session. An evaluation technique of the dataflow through the network was carried out. The captured transmission parameters offer an inbound and outbound limit of dataflow through which the AGVs communicate with each other. The findings of this paper indicate that the ideal transmission rates at the frequency of 434 MHz and at a baud rate of 19200 bps was found to be 25 ms in between each 56-B data packets. The range of distance between the transmitter and the receiver was 0.5 to 970 m. The transmitter had a 1-km range limitation. As the applications for which the communication model was developed did not require long distances, the transmitter's range limitation was sufficient. Further tests validated these transmission session parameters values. The proposed techniques can be implemented as logistic and automation solutions in the manufacturing industry.

Germanium–antimony–telluride has emerged as a nonvolatile phase change memory material due to the large resistivity contrast between amorphous and crystalline states, rapid crystallization, and cyclic endurance. Improving thermal phase stability, however, has necessitated further alloying with optional addition of a quaternary species (e.g., C). Here, the thermal transport implications of this additional species are investigated using frequency-domain thermoreflectance in combination with structural characterization derived from x-ray diffraction and Raman spectroscopy. Specifically, the room temperature thermal conductivity and heat capacity of ( Ge 2 Sb 2 Te 5 ) 1 − x C x are reported as a function of carbon concentration ( x ≤ 0.12) and anneal temperature ( T ≤ 350 ° C) with results assessed in reference to the measured phase, structure, and electronic resistivity. Phase stability imparted by the carbon comes with comparatively low thermal penalty as materials exhibiting similar levels of crystallinity have comparable thermal conductivity despite the addition of carbon. The additional thermal stability provided by the carbon does, however, necessitate higher anneal temperatures to achieve similar levels of structural order.

Frequency domain thermoreflectance (FDTR) is used to create quantitative maps of thermal conductivity and thickness for a thinning gallium nitride (GaN) film on silicon carbide (SiC). GaN was grown by molecular beam epitaxy on a 4H-SiC substrate with a gradient in the film thickness found near the edge of the chip. The sample was then coated with a 5 nm nickel adhesion layer and a 85 nm gold transducer layer for the FDTR measurement. A piezo stage raster scans the sample to create phase images at different frequencies. For each pixel, a periodically modulated continuous-wave laser (the red pump beam) is focused to a Gaussian spot, less than 2 um in diameter, to locally heat the sample, while a second beam (the green probe beam) monitors the surface temperature through a proportional change in the reflectivity of gold. The pump beam is modulated simultaneously at six frequencies and the thermal conductivity and thickness of the GaN film are extracted by minimizing the error between the measured probe phase lag at each frequency and an analytical solution to the heat diffusion equation in a multilayer stack of materials. A scanning electron microscope image verifies the thinning GaN. We mark the imaged area with a red box. A schematic of the GaN sample in our measurement system is shown in the top right corner, along with the two fitting properties highlighted with a red box. We show the six phase images and the two obtained property maps: thickness and thermal conductivity of the GaN. Our results indicate a thickness dependent thermal conductivity of GaN, which has implications of thermal management in GaN-based high electron mobility transistors.

Frequency domain thermoreflectance (FDTR) imaging is used to create quantitative thermal conductivity maps of porous Aluminum Nitride (AlN) particles embedded in epoxy. The AlN-epoxy composite is polished and coated with a metal layer. A piezo stage is used to move the sample for imaging with our FDTR system. For each pixel, a periodically modulated continuous-wave laser (the red pump beam) is focused to a Gaussian spot, less than 2 um in diameter, to locally heat the sample, while a second beam (the green probe beam) monitors the surface temperature through a proportional change in the metals' reflectivity. The pump beam is modulated simultaneously at six frequencies and the thermal properties of the AlN composite are extracted by minimizing the error between the measured probe phase lag at each frequency and an analytical solution to the heat diffusion equation in a multilayer stack of materials. A schematic of the AlN sample in our measurement system and an optical image of the polished surface of the AlN-epoxy composite before coating with metal is shown in a. Two scanning electron microscope images of the porous AlN particles prior to embedding in epoxy are shown in b. One of the six simultaneously collected phase images of the probe laser is shown in c. The dark blue regions in the phase image are pits on the sample surface. We fit the six phase images to our thermal model and obtain thermal conductivity maps. The conductivity maps of four particles are shown in d. A log color bar is used to highlight the contrast of thermal conductivity in a single particle. The thermal conductivity of the AlN particles ranges from 80W/mK in the dense regions to 5W/mK in the porous regions.

Frequency domain thermoreflectance (FDTR) imaging is used to create quantitative maps of both in-plane thermal conductance and cross-plane thermal boundary conductance (TBC) for graphene multilayers encased between titanium and silicon dioxide. A graphene flake is encased between a metal layer and a thermally oxidized p-type silicon wafer and a piezo stage is used to raster scan the sample for imaging. For each image pixel, a periodically modulated continuous-wave laser (the red pump beam) is focused to a Gaussian spot, less than 2 um in diameter, that locally heats the sample, while a second beam (the green probe beam) monitors the surface temperature through a proportional change in reflectivity. The pump beam is modulated simultaneously at six frequencies and the thermal properties of the graphene flake are extracted by minimizing the error between the measured probe phase lag at each frequency and an analytical solution to the heat diffusion equation in a multilayer stack of materials. Phase images at six frequencies for the sample are shown in b. Different layers of the graphene flake are clearly shown in 9.9 MHz and 11.3 MHz images. The six phase data points at every pixel are then fitted to our thermal model to generate two thermal property maps of the graphene flake: in-plane thermal conductance and TBC, shown in c. The in-plane thermal conductance map shows an increased conduction of heat in graphene with the number of layers, while the TBC map indicates a constant cross-plane conduction along the flake. Our imaging technique can be used to study thermal transport in graphene and has implications for thermal management in graphene based electronic devices.