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Fabrication process determines the composite quality. Conventional method such as dry- and hand lay-up are commonly used. Dry lay-up method has known to be more controllable and produce less defect composites with good mechanical property. However, this method is more expensive. On the other hand, hand lay-up which is more simple and less expensive, is uncontrollable as well as produces more defect and poorer mechanical properties of composites. In this study, we creates instrument which is able to control wet lay-up fabrication process of Fiber Reinforced Composite Material (FRCM). Instead of using uncontrollable human hands, this instrument utilizes speed controllable paint roller which distributes the resin though all matrix. The result shows that the produced composites have more homogenous resin distribution, smaller size defects, and exhibits stronger mechanical properties compare to the one produced by hand lay-up method. This study is expected to open further innovations on low cost composite fabrication.

Conventional bricks are manufactured from clay with high firing temperatures. However, this method results in the depletion of clay and an increase in energy consumption. In addition, biomass lignocellulosic waste such as corn also increased along with population growth. Some studies reported the utilization of corn lignocellulosic waste to protect the environment in the biomass refinery. Therefore, this study aimed to examine the potential of corn lignocellulosic waste addition in the fired clay bricks production. The mixing of clay/corn lignocellulosic waste (500 µm size) with a ratio of 2.5% of the total weight of bricks was used in the manufacturing of fired brick. The raw bricks were then burned by using a temperature of 600 °C. Then, the influences of corn lignocellulosic waste impregnation fired clay brick was examined in terms of density, porosity, and compressive strength. The density of the mixture of clay/corn lignocellulosic waste brick was lower than clay brick, 1.437 gram/cm3 versus 1.521 gram/cm3, respectively. The porosity of the mixture of clay/corn lignocellulosic waste brick was lower than clay brick, 27.3% versus 35.79% respectively. However, the compressive strength of the mixture of clay/corn lignocellulosic waste brick was higher than clay brick, 6.81 MPa versus 4.15 MPa, respectively. This study showed that corn lignocellulosic waste has the potential as partial replacement of conventional raw bricks that the standard requirements were applied.

Photonic band gap tunability is crucial in designing optoelectronic devices. Nanostructure semiconductors with tunable band gaps which depend on the dimensionality, have become the potential candidate for tunable nano optoelectronic devices. However, it has a lot of challenges in their fabrication such as the limited number of homogenous particles and high-cost production. As an alternative, sub-micrometer particles with the order of hundred nanometers are more easily fabricated and exhibit tunable optoelectronic properties. In this study, sub-micrometer WS2 was fabricated using low-cost electrochemical methods. Two clusters of particles with the average size of 100 nm and 600 nm are observed. The number of sub-micrometer particles increases with the increasing of fabrication time. The photoluminescence spectra show wide peak centered around 800 nm suggesting the possible application in visible light emitting devices. The peak position varies with the time variation showing that the optical properties might be tuned during fabrication. This study points out that simple solution processed fabrication method can produce sub micrometer particles with tunable optical properties.

Di masa pandemi seperti sekarang ini, kesehatan dan kondisi ekonomi masyarakat perlu mendapat perhatian lebih. Sebagaimana masyarakat umum lainnya, warga Desa Citeureup juga merasakan dampak pandemik ini. Sebagian warga ada yang terinfeksi Covid 19 dan sebagian lagi kehilangan pekerjaan atau usahanya harus dihentikan akibatnya adanya pembatasan maupun menurunya jumlah omset usahanya. Berdasarkan pertimbangan tersebut, Tim Dosen Teknik Fisika Universitas Telkom melakukan pengabdian masyarakat di RW 6 Desa Citeureup. Kegiatan dilakukan dalam bentuk survey untuk memetakan persoalan di masyarakat, pemasangan tempat cuci tangan, dan pelatihan keterampilan pembuatan sabun cair. Hasil survey menunjukkan bahwa masyarakat secara umum terdampak oleh Covid 19 dan menginginkan adanya bantuan agar mereka memiliki usaha sendiri. Kegiatan ini diharapkan menjadi kampanye peningkatan kesadaran masyarakat akan pentingnya kebersihan dan kesehatan, transfer pengetahuan tentang pembuatan sabun cair, dan inisiasi kemandirian ekonomi masyarakat desa Citeureup.

WS2 is two-dimensional layered material which the electronic band gap is dependent on the number of layers. From application point of view, the WS2 few layers are good candidate for nano scale flexible electronics . In this study, the WS2 number of layers is modified using liquid phase exfoliation method. The blue shift of WS2 supernatant absorption peaks suggested the change of layer thickness compare to the non-exfoliated one. This supernatant is further deposited on Polyethylene terephthalate (PET) to create a flexible multilayer WS2 thin films. The morphology and the content of the thin film are confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS), respectively. The Raman and photoluminescence spectroscopy show typical characteristics of WS2 multilayers which are dominated by W-S vibrations, exciton contributions, as well as the local defect and strain effects. Furthermore, the electrical characterization reveals the robustness of the WS2 electronic properties again the mechanical stretching. This study highlights the abundant optical and electrical characterization of WS2 multilayer which are applicable for flexible electronic devices.

Two-dimensional (2D) layered materials transition metal dichalcogenide compound (TMDC), which stack-together and form van der Waals heterostructures, have created interesting phenomena due to their interlayer interactions and their great potential for atomic-scale devices. Various electrical properties have been investigated. The presence of vacancies and their related charge trappings have been reported to affect the electrical properties. In this study, we investigate the electrical properties of hybrid WS2/MoS2 multilayer film deposited on polyethylene terephthalate (PET). The hybrid morphology and signatures are confirmed by the scanning electron microscope image and Raman shift spectra, respectively. We observed a semiconductor like behaviour as well as the large hysteresis which indicates the vacancies inducing charge trappings. This characteristics is different with the electronic characteristics of WS2 and MoS2 multilayer which tend to exhibit insulating behaviours and small hysteresis. This study shows how hybrid dichalcogenide WS2/MoS2 multilayer might create new features for future electronic devices.

The dream to have multifunctional materials has triggered an intense study of multiferroicity,i.e.of materials in which magnetic and electric polarizations are simultaneously present and strongly coupled. Here we study TbMnO3, a perovskite manganite exhibiting multiferroicity. It has an incommensurate antiferromagnetic ordering transition at 41 K and a transition into a multiferroic spin spiral state at 26 K. In this study, Raman spectroscopy has been used to elucidate the nature of the excitations related to phase transitions. We show that the optical phonons in TbMnO3resemble the phonon characteristics typical for perovskite manganites, corresponding to MnO6octahedral vibrations. The appearance of a new low energy modes at 32 cm-1, 40 cm-1, and 63 cm-1observed below 41 K signifies the antiferromagentic ordering in TbMnO3. The 32 cm- 1and 63 cm-1are interpreted as spin ordering activated phonon while the 40 cm-1is interpreted as spin ordering induced splitting of Tb quasi doublet cystal field level.

In this study, PID controller instrument design for controlling the input current to thermoelectric cooler (TEC). For cooling process, we used thermoelectric type of 12706 with active material of Bi2Te3. The instrument was tested by comparing the cooling process with and without PID control. Without PID control, the TEC modules cooled the temperature down to 11 “C within 6538 seconds. This temperature was obtained within 2060 seconds when PID control was applied. This finding showed that PID control could accelerate three times faster the cooling process. The best parameters for controlling were K p =8.5, K i =1.9 and K d =0.4. In addition, we observed that two serial modules of TEC with current input of 2A could reach a set point of 11 °C. This result was better than a cooling process using three individual TEC modules in which each module was driven by 6A current. Our results showed that beside the number of TEC modules, the heat distribution also played important role in cooling process. Since two serial modules dissipated less power than three individual modules, the heat distribution became more effective and similar temperature could be achieve.

We have studied the magnetoelectric coupling of the frustrated triangular antiferromagnet iron jarosite using Raman spectroscopy, dielectric measurements and specific heat. Temperature dependent capacitance measurements show an anomaly in the dielectric constant at T-N. Specific heat data indicate the presence of a low frequency Einstein mode at low temperature. Raman spectroscopy confirms the presence of a new mode below T-N that can be attributed to folding of the Brillouin zone. This mode shifts and sharpens below T-N. We evaluate the strength of the magnetoelectric coupling using the symmetry unrestricted biquadratic magnetoelectric terms in the free energy. (C) 2012 Elsevier Inc. All rights reserved.

A Raman spectroscopy study on the half-doped single-layer manganite Pr0.5Ca1.5MnO4 has been performed in combination with x-ray diffraction, resistivity, magnetization, and specific heat measurements. The results provide insight into the underlying mechanisms of phenomena that arise from correlations between lattice, charge, orbital, and spin degrees of freedom. The appearance of a new Raman mode at 366 cm(-1), a visible jump in the resistivity, and a doubling of the unit cell signify the onset of charge/orbital ordering at 320 K. This transition is also marked by a sharp peak in the magnetic susceptibility and specific heat, suggesting strong spin-charge coupling. Our structural analysis suggests that the charge disproportionation below 320 K is small. Orbital fluctuations below 320 K are evidenced by the evolution with temperature of the Jahn-Teller Raman mode (situated at 533 cm(-1) at 320 K). A coincidence between the onset of two-dimensional short-range antiferromagnetic order at 215 K and anomalies in both the temperature dependence of the Jahn-Teller mode and the Mn-O bonding pattern in the ab plane indicate that the short-range magnetic order plays a role in stabilizing the orbital fluctuations. Below the Neel temperature of 127 K, the softening of both the 366 cm(-1) mode and an octahedral tilting mode at 214 cm(-1) mark the onset of three-dimensional antiferromagnetic ordering. The estimated spin-phonon coupling constants for these two modes are 2.6 and 6.8 cm(-1), respectively. This study highlights the remarkable coupling of charge, orbital, and spin degrees of freedom to the lattice in single-layer Pr0.5Ca1.5MnO4.

Computer has been part of our daily life. In order to work properly and to avoid over heating which might damage the machine, it required a cooling system which effectively distribute heat from the electronic devices into surrounding environment. Generally, the cooling system only distributes the heat. The potential heat conversion into electricity in computer has not been studied intensively. In this study, we implement a thermoelectric generator module which converts heat into electicity in combination with hybrid cooling system on CPU processor, a main crucial part in computer system which produces a lot of heat and its work is very temperature dependent., We used a thermoelectric module TEG1 241-1.0-12 which can generate electricity up to 12.1 volt at temperature difference of 110 °C and Seebeck coefficient from 35 mV/οC up to 45 mV/οC. The available size of thermoelectric module is found to be matched with the CPU processor and the hybrid heat sink structure so that no structural adjustment is required. We used hybrid cooling system of PC Cooler Hybrid W120 which consists of an aluminium heat sink and water cooling with flow rate of 6.7 liters/minute. We found that a 2.5 V and 0.19 A (≈ 0.5 W) electricity can be generated when a thermoelectrics module is implemented in Intel Core i3-2100 microprocessor. The observed different temperature between hot and cold sides of thermoelectric is 54 °C while the processor temperature is 80 °C. This study shows the potential implementation of thermoelectric for heat conversion into electricity on CPU processor without endangers the machine.

We propose a non-resonant two-photon absorption as a method to create a high-density gas of para-excitons uniformly distributed in a whole volume of a crystal. In non-linear pump–probe experiments we measure changes of the IR absorption induced by the presence of optically excited para-excitons. This way, we directly determine the energy of the para-excitonic 1 s → 2 p transition at 129 meV. On the basis of temporal evolution of the induced absorption signal we find the lifetime of the para-excitons to be of the order of 10 ms.

Determining the magnetic order of solids in high magnetic fields is technologically challenging. Here we probe the cascade of magnetic phase transitions in frustrated multiferroic CuFeO2 using nuclear forward scattering (NFS) in pulsed magnetic fields up to 30 T. Our results are in excellent agreement with detailed neutron diffraction experiments, currently limited to 15 T, while providing experimental confirmation of the proposed higher field phases for both H parallel to c and H perpendicular to c. We thus establish NFS as a valuable tool for spin structure studies in very high fields, both complementing and expanding on the applicability of existing techniques.

We study the temperature dependence as well as anisotropy of optical conductivity (${\ensuremath{\sigma}}_{1}$) in the pseudocubic single crystal Pr${}_{0.5}$Ca${}_{1.5}$MnO${}_{4}$ using spectrocopic ellipsometry. Three transition temperatures are observed and can be linked to charge-orbital (${T}_{\mathrm{CO}/\mathrm{OO}}\ensuremath{\sim}$320 K), two-dimensional-antiferromagnetic (2D-AFM) ($\ensuremath{\sim}$200 K), and three-dimensional AFM (${T}_{\mathrm{N}}\ensuremath{\sim}$125 K) orderings. Below ${T}_{\mathrm{CO}/\mathrm{OO}}$, ${\ensuremath{\sigma}}_{1}$ shows a charge-ordering peak ($\ensuremath{\sim}$0.8 eV) with a significant blue shift as the temperature decreases. Calculations based on a model that incorporates a static Jahn-Teller distortion and assumes the existence of a local charge imbalance between two different sublattices support this assignment and explain the blue shift. This view is further supported by the partial spectral weight analysis showing the onset of optical anisotropy at ${T}_{\mathrm{CO}/\mathrm{OO}}$ in the charge-ordering region (0.5--2.5 eV). Interestingly, in the charge-transfer region (2.5--4 eV), the spectral weight shows anomalies around the ${T}_{2\mathrm{D}\ensuremath{-}\mathrm{AFM}}$ that we attribute to the role of oxygen-$p$ orbitals in stabilizing the CE-type magnetic ordering. Our result shows the importance of spin, charge, orbital, and lattice degrees of freedom in this layered manganite.

Time resolved optical spectroscopy is used to elucidate the dynamics of photodoped spin-aligned carriers in the presence of an underlying magnetic lattice in the multiferroic compound TbMnO3. The transient responses while probing d-d intersite transitions show marked differences along different crystallographic directions, which are discussed in terms of the interplay between the processes of hopping of the photo-injected electrons and the magnetic order in the material.

The phonon and crystal field excitations in several rare earth titanate pyrochlores are investigated. Magnetic measurements on single crystals of Gd2Ti2O7, Tb2Ti2O7, Dy2Ti2O7 and Ho2Ti2O7 are used for characterization, while Raman spectroscopy and terahertz time domain spectroscopy are employed to probe the excitations of the materials. The lattice excitations are found to be analogous across the compounds over the whole temperature range investigated (295-4 K). The resulting full phononic characterization of the R2Ti2O7 pyrochlore structure is then used to identify crystal field excitations observed in the materials. Several crystal field excitations have been observed in Tb2Ti2O7 in Raman spectroscopy for the first time, among which all of the previously reported excitations. The presence of additional crystal field excitations, however, suggests the presence of two inequivalent Tb3+ sites in the low temperature structure. Furthermore, the crystal field level at approximately 13 cm-1 is found to be both Raman and dipole active, indicating broken inversion symmetry in the system and thus undermining its current symmetry interpretation. In addition, evidence is found for a significant crystal field-phonon coupling in Tb2Ti2O7. These findings call for a careful reassessment of the low temperature structure of Tb2Ti2O7, which may serve to improve its theoretical understanding., 13 pages, 7 figures

This research is aimed to analyze and simulate the temperature distribution in heat sink CPU processor. The study analyzes the heat absorption from the heat source to the bottom of the heat sink, the conduction process, and the forced convection process. All processes are simulated with software Comsol Multiphysics 4.4 to obtain the optimal heat sink design. The simulation is performed by varying the number of fins, the fin thickness, the air gap between two fins, the fin surface area, and the convection coefficient. The optimal design is found for heat sink with 40 pieces fins, fin thickness of 0.4 mm, air gap of 2.4 mm, fin surface area of 9425 mm2, and the convection coefficient of 5.26 W/m2K. Further simulation shows that PID control improved the forced convection process. A proportional control (P) is reasonable enough to achieve a settled convection process. A settling temperature occurs at 241 s after heat is applied to the system. This is faster than non-controlled convection process which requires 1600 s instead. Additional integration and derivative controls will increase stability at later time.