The operational stability of halide perovskite solar cells (HaPSCs) is imperative for their commercialization. Although HaPSCs have almost reached the climax of device performance, their long-term operational stability remains a primary challenge for real-world applications. Despite significant progress through engineering the bulk and the interface layer in device configuration, the mechanisms underlying the degradation of HaPSCs under continuous illumination and stress are still ambiguous. Our work suggests that degradation is initiated mainly by the deterioration of the HaP bulk at columnar inter-grains and the interfacial junction with the release of I2�gas, which worsens the interface quality. In this talk, we will discuss the degradation mechanisms by post-mortem analysis of HaPSCs aged under heat and maximum light conditions.

Photovoltaic is one of the fastest growing renewable energy technologies. Organic-inorganic perovskite photovoltaics are at the center of semiconductor research due to low cost, solution processing and high performance in the last decade. However, challenges in the performance remains due to polycrystalline nature of perovskite films that is susceptible to surface and grain boundary defects. Defect passivation and enhancement of charge carrier dynamics can be better approach to further increase the power conversion efficiency. We studied the hydrazine-based aromatic iodide salt or phenyl hydrazinium iodide (PHI) for secondary post treatment to passivate the defects at surface and grain boundary in perovskite thin films. The PHI post treatment contributed to current reduction at the grain boundaries, facilitated an electron barrier, and reduced the trap state density which corresponds suppression in leakage pathways and the charge recombination, hence passivating the grain boundaries. As a result, a significant improvement from 17.4% to 20.6% in power conversion was obtained for the PHI treated perovskite device in comparison to a control device.

We report high energy density thin film capacitor composed of chemically inert oxides of abundant elements developed using atomic layer deposition (ALD) technique. We fabricated and studied thin film capacitors with multi-stacked Al2O3/TiO2 nanolaminate (~150 nm) deposited by ALD technique on both rigid and flexible substrates. The stacking of thin layers of these oxides results in a dielectric constant value that is higher than one or two orders of magnitude higher than the individual oxides used due to a process known as Maxwell Wagner relaxation. While these nanolaminate oxides have high dielectric constant, thin films are known to have pinholes that becomes a bottleneck to scale up thin film capacitors. The ALD technique fulfills the need of pinhole-free high quality ultra-thin film using sequential and self-limiting surface reactions. Also, this technique is proved to produce uniform and conformal coating on high aspect ratio structures, which thus allows us to coat these dielectric nanolaminates in high surface area electrodes to further increase the energy density. By using substrate cleaning, electrode metal treatment, and optimization of the ALD recipe, we are able to minimize the pinholes and improve the yield to 90%. On a planar substrate, these capacitors have the specific capacitance of ~1.6 ?F/cm2 and breakdown voltage of 3 V (~2 x105 V/cm) with 10 ?A leakage current. Our nanolaminate capacitors coated on copper plates were employed in electrocardiogram (ECG) monitor to replace traditional gel contact electrode to pick up human ECG signal, and we were able to show good performance. Coating these nanolaminates on ZnO nanorods increased the specific capacitance but the device became more leaky due to the randomly entangled nanorods. Our future effort will be to develop well-ordered nanostructured electrode to minimize leakage and increase energy density.

The solidification process of Sn is vital in the formation of lead-free tin-based interconnects. Electronic packages contain billions of solder joints. Tin is a significant portion of these lead-free solder joints. These solder joints are melted, cooled, and solidified during the fabrication of modern electronic devices. When liquid Sn above melting temperature is cooled, ?-Sn nucleates below its melting temperature. Due to the low symmetry of the Sn crystal, Sn nucleates with incredible difficulty. The nucleation and growth of the Sn determine the microstructure of these solder joints and affect the mechanical properties of these solders, and finally affect the performance of devices containing these joints. Hence it is very important to understand the poorly understood nucleation phenomena in these Sn-based Pb-free solder joints.

The nucleation of Sn is affected by the heterogeneities present in it. Here Ni was alloyed with Sn to study the effect of heterogeneity on the nucleation of Sn. In addition, it was sought to control the levels of Ni in Sn and measure the kinetics of Sn as a function of temperature within the context of classical nucleation theory. Calorimetric examination of various Ni amounts in Sn showed the increase in solidification temperature of Sn with the rise in Ni concentration in Sn. These solidification temperatures were statistically analyzed to obtain the nucleation rate in these Sn-Ni systems. The huge increase in nucleation rate of Sn was noticed with the increase in Ni percentage in Sn. Such a drastic increase in nucleation kinetics corresponds to the decline in the energy barrier to nucleation. This decline in energy barrier to nucleation could be explained by a decrease in wetting angle and interfacial tension between solid and liquid.

Human society is an open system that evolves by coupling various known and unknown fluxes. How does this complex system dynamics precisely unfold? A science of human society may provide further insights. The evolution of our civilization has depended largely on cooperation among human beings. However, our science is yet to figure out �How did cooperative behavior evolve?� This question [1] from the ‘What don�t we know� series from the Science journal has been awaiting physical reasoning for a long time. We generalize the classical field theories for an ensemble of human beings and proposed the social field theory [2]. The social field theory formalizes the social force and the Hamiltonian of an individual in the social field. We underpin this new Hamiltonian as a physical basis for cooperation among human beings and the evolution of human society. With the Hamiltonian defined [3], we use the Navier-Stokes� approach to study the dynamics in the social field that evolves with time. The equations for the evolution of an individual and human society are sketched based on the time-dependent Hamiltonian that includes the power dynamics. Lotka-Volterra type equations can be derived from the Hamiltonian equation in the social field.

A fundamental understanding of why cooperation evolved may have a resounding effect on our understanding of social, political, and economic rationale. Indeed, Darwin uncovered some ideas of cooperation in his theory of evolution. However, the science of evolution doesn’t provide physical reasoning, and also not adequate for 21st-century reasoning. Biologists are refining Darwin’s ideas a bit by bit. Here, we aspire to uncover the science of cooperation and many social dynamics in terms of the Hamilton of an individual in the social field. Human cooperation is not much different literally from cooperation that takes place between an electron and nucleons in a model of the Hydrogen atom. It is our consciousness that makes human cooperation special among social beings.

We speculate on some possible directions in which the science of human society may develop over the next few decades, especially by connecting the natural and social sciences, the two eyes of our human knowledge. Money is a concept of paramount significance to economic science, social science in general. This new framework conceives of money following the original insights of Howard Odum [4]. These concepts may bring forth a useful connection between the sciences at the fundamental level. Even if the field-based approach based on homology may supply important insights to the core economic concept such as capital, development, business cycles, etc., there are still many important questions at the intersection of the two cultures [5] to which we currently have no satisfactory answers. We believe that a two-eyed approach may inform some important questions at the crossroads of the natural and social sciences in the 21st century.

Nepal mostly comprises of hilly and mountainous terrain and susceptible to elongated periods of acute cold. As a result, not only the locals but also more than 2 hundred thousand trekkers and mountaineers suffer with diseases associated with coldness (e.g., pneumonia). To address this issue in a sustainable way, we have for the first time devised a palm-sized hand warmer from the composite of varieties of nanomaterials and phase change material (PCM)1,2. Our product can store solar energy which can be utilized in the form of heat when needed. As demonstrated in Fig.1, once it is charged (fully melted), the stored solar energy can be released back as thermal energy just by triggering a mechanical button embedded inside the handwarmer system. Among tested composite of copper oxide and sodium acetate trihydrate (SAT) found to be the most effective system, considering its charging and its thermal performance. The handwarmer can produce heat of max. 55 oC at the beginning and can last for heat for an hour (i.e., it takes an hour to come to the room temperature)3. Being handy and environmentally friendly, we believe that the product will be useful for motorbike riders, mountain travelers, and mountain dwellers in the winter season.

Keywords: Nanomaterials, Phase change material, Sodium acetate trihydrate, solar energy storage system, hand warmer

REFERENCES

(1) Miro?, L.; et al., Thermal Energy Storage (TES) for Industrial Waste Heat (IWH) Recovery: A Review. Appl. Energy 2016, 179, 284?301.

(2) Englmair, G.; et. Al., Solar Combi-System Utilizing Stable Supercooling of Sodium Acetate Trihydrate for Heat Storage: Numerical Performance Investigation. Appl. Energy 2019, 242, 1108?1120.

(3) Kafle, B. P..; Storing Solar Energy in Sodium Acetate Based Hand Warmer Using Light Absorbing Particles, ACS Appl. Energy Mater. 3 (2020) 11772 �11780.

Recently, many non-volatile memory devices such as resistive random-access memory (RRAM) have been investigated for analog in-memory computing applications related to inference and training in artificial intelligence. RRAM devices are non-volatile and have the advantages of high density and high-speed. A RRAM cell has an MIM (metal insulator metal) structure that exhibits reversible resistive switching on application of positive or negative voltage. The switching properties of the dielectric is controlled by formation and dissolution of a conductive filament within the insulating/dielectric layer that switches the device between low resistance and high resistance states. The states can be considered as zero and one as in digital electronics. By carefully managing the applied voltage pulse multi-level operation can be achieved. This behavior can be explored in neuromorphic computing to implement the synaptic weights. However, power consumption in the existing RRAMs is significantly high for low power applications. HfO2-based dielectrics with controlled distribution of defects or oxygen vacancies can potentially enable low power switching and multi-resistance levels. In this work we present detailed analysis of power consumption and repeatability during multi-level operation.

Hydrophobic surfaces are the surface having the contact of angle greater than 90o. ZnO thin films were prepared by using a simple method of Precipitation method which were prepared using the paste of ZnO of variable molarity (0.2M,0.5M) with Zinc Acetate Dihydrate (ZnC4H6O4.H2O), Monoethanolamine (C2H7NO), Distilled Water (H2O) and 2-Methoxyethanol (C3H8O2) which were deposited on normal transparent glass substrate by Spray Pyrolysis Coating at 450oC. The contact angle was measured by using goniometer (105o) and the crystallographic structure of ZnO was characterized by XRD (X-ray diffraction). It was found that the coated layer of ZnO on glass improves the hydrophobicity of the glass repelling the water droplets. There is going on wide range of research work on hydrophobic and super-hydrophobic coating which bring the outstanding application of it in various field. The research work emphasis the future work and development in respective field.

The force experienced by hamstring during leg curl has been studied using the conservation theorem. It is assumed that the center of meniscus is taken as pivot point and uniform distribution of forces with frictionless environment. The variation of force experienced by hamstring during concentric motion of leg curl is derived based on the Newton’s law of motion and conservation of energy theorem. The force experienced by hamstring increases with the increase in length of lower leg and its weight. With the increase in weight of lower leg, the magnitude of force increases from about 4.2 kN to 4.8 kN at length of lower leg 45 cm. The magnitude of force increases with the increase in weight suspended on machine, although it decreases with the increase in distance between pivot and insertion. In addition, the force decreases with the increase in upper leg dimension, but it linearly increases with the increase in angle of suspension.

The word CASWAT-G stands for Circulating Cable Supported Up-Down Walking Technology by Using Gravity. This is a class of surface ropeway which can be considered as CASWAT-G Transportation System (CTS) that is useful for the mobility of the mountainous people. The system is somehow similar to surface transportation systems like funicular, ski-lift, rock climbing rope securing technique in which (beside ski-lift) force harvested from descending load or person is utilized to pull ascending person up on the surface of the slope land.

Hard effortful up and down walking against and towards the gravitational field in a slope land can be overcome by harvesting gravitational force(GF) of descending person(DP) by using newly developed CASWAT?G surface ropeway. In the machine, circulating cable (CC) circulates between two bull wheels fixed on the top and the base of a hill. For two users (i. e. one walking up and the other down) using the system, we can consider the case that they start walking one from the top and the other from the base of a mountain hill. On connecting both of them to the CC by a body connecting cable (BCC) and taking support of BCC, there will be balance of forces they harvest from their own body and frictional force in the system and it will keep them at rest. When they start walking, the harvested force of DP will pull ascending person (AP) up.

From the various experimental prototype tests as well as theoretical models it is verified that this type of system is simple, cheap, eco-friendly and requires very comfortable effort to walk up and down with negligible destruction of the natural environment.

The Ratuwa river is a major source of surface water and is used for different purposes. The contaminated water is directly or indirectly related to health hazards. Therefore, this work is greatly concerned to evaluate the spatial variation of water quality index of the Ratuwa river allowing comparisons with future studies. The water samples were collected from six sampling sites of Ratuwa river including tributary rivers and then tested fifteen parameters by using respective well-calibrated equipment and standard APHA methods. The WQI was evaluated with thirteen parameters by using the weighted arithmetic method as it depicts overall water quality status in single terms. The WQI of R01, R02, R03, R04, R05, and R06 were 69.122, 38.453, 55.890, 52.403, 51.204, and 67.711 respectively which falls in a range of good to poor quality of water. Also, Pearson�s correlation matrix has been drawn using Origin Pro 8 software to find the potential parameters for degrading water quality. The result shows that Electrical Conductivity (EC), Total Dissolved Solids (TDS), and Total Alkalinity (TA) have a higher positive correlation with WQI. The rest of the parameters have a weak positive correlation with WQI except chloride and potassium since they have a weak negative correlation with WQI.

Keywords: Spatial variation, Water quality index, Pearson�s correlation matrix