PISIKA - Journal of the Physics Society of the Philippines

Spatio-temporal validation of interpolated rainfall measurements from Philippine synoptic stations

2019-02-04T02:03:42+08:00

Rainfall measurements from synoptic stations in the Philippines were subjected to kriging and iterative method to create a gridded interpolated rainfall measurements of 0.25° resolution. The interpolated measurements were compared to TRMM rainfall data product for the years 2008 to 2017. It was found out that significant correlation and mutual information were present for both datasets in Luzon and Visayas. Moreover, ground measurements from agrometeorological stations were used to verify reliability of interpolated measurements in Mindanao. It was found out that little correlation exists between the two, with mutual information suggesting independence from both datasets.

Linear chemical potential leading to a closed form of the magnetization of a 2DEG in a perpendicular magnetic field

2019-02-04T02:03:33+08:00

A two-dimensional electron gas (2DEG) under a perpendicular magnetic field is considered. For a given Landau level, the chemical potential can be approximated to have a linear dependence on the magnetic field. This approximation is valid except when complete filling is reached (integer filling factor). The chemical potential oscillation yields a recursion relation for every Landau level. This gives way to an exact form of the magnetization. The derivations herein hold at low temperature.

Towards a more eﬃcient scheduling of regular NBA games

2019-02-04T02:03:25+08:00

Finding the optimal schedule for the 82 games played by each of its 32 teams in a regular season is a continuing challenge for the National Basketball Association (NBA). We examine the schedules of the regular NBA games in the last 22 seasons including the current one to ﬁnd possible trends in its key parameters - distance traveled during road games and number of successive (e.g. back-to-back) games played. To reduce operational cost and to keep a level playing ﬁeld, the total distance traveled and the number of back-to-back games must be kept to a minimal and the same for all teams. Data have shown that teams are unlikely to win twice in back-to-back games. We implement a scheduling algorithm that aims to minimize a cost function that incorporates the key parameters as its variables. For the same season duration, the algorithm has been able to reduce the number of back-to-back games by 24% while increasing the total distance traveled by 25%.

Obtaining pre-alarm thresholds for deep-seated landslides using receiver operating characteristic convex hull analysis of slope kinematics

2019-02-04T02:03:17+08:00

Early warning systems for deep-seated landslides are recommended to have three levels; ordinary, pre-alarm,
and alarm. Defining landslide kinematics threshold values for each level is difficult due to the large variability
of geological and meteorological conditions of each site, coupled with the social implications of false and missed
alerts. Although historical pre-failure values of velocity and acceleration may be used as thresholds for the
alarm level, thresholds for pre-alarm level are indefinite since it is based only on the seasonal oscillations of
the landslide displacement. To create a systematic and robust method of defining pre-alarm threshold values
based on historical values of displacement, we evaluate the performance of four different landslide kinematic
thresholds namely, displacement, average velocity, spline computed velocity, and spline computed acceleration,
in predicting landslide acceleration using receiver operating characteristic convex hull analysis. We select the
optimal parameter depending on the cost of false and missed alerts. We use the ground data of the 50 identified
deep-seated landslide risk sites of the Philippine Institute of Volcanology and Seismology - Dynaslope Project
to evaluate the performance of these parameters. We found that the spline computed quantities provide the
optimal parameter for majority of the displacement data. The obtained threshold values were consistent in
order of magnitude demonstrating the robustness of the method. In future studies, other external landslide
triggering factors may be included in the selection process.

Action potential initiation and propagation in a branching dendritic model of CA3 pyramidal neuron

2019-02-04T02:02:38+08:00

In this study, the signal transmission and the spiking patterns of a CA3 pyramidal neuron were simulated through a 69-compartment model with branching dendritic structure. For the simulation, we numerically solved coupled first-order nonlinear ordinary differential equations using fourth order Runge-Kutta method with step size of 2.5×10^-3ms. By introducing steady current into the soma, action potentials (APs) were induced. Results reveal two main firing properties of CA3 pyramidal neuron under constant stimulation current: spike frequency adaptation and intrinsic bursting. Results also show AP is initiated in the axon-initial segment 12.5µm - 87.75µm from the center of the soma and propagated retrogradely (backpropagation) into the dendrites. APs propagated in the axon displayed no attenuation while APs backpropagated in dendrites demonstrated decrease in amplitude and increase in spike duration. The calculated backpropagation ratio, (15.6±0.18) × 10^-2, suggests that backpropagating APs underwent significant attenuation.

Trends in the spread of global news in the English language

2020-02-24T02:13:54+08:00

Analyzing the flow of news across national boundaries can increase our understanding of a country's perspective of the global scene. This paper utilized the GDELT Project's database of English news articles to determine the trends in the global coverage of international news topics. The distributions of the time delays before a country catches on a particular news topic were studied. It was found that major countries, such as the United States, and countries with an English-speaking population generally have smaller time delays in publishing articles written in the English language. By using average linkage hierarchical clustering, common trends in the distributions of publishing time lags were determined and countries following the same patterns were found. The clustering of these distributions correlate with the geographical proximity of the countries.

Identifying optimal earthquake evacuation routes using genetic algorithm

2019-02-04T02:02:08+08:00

The disaster response team of Metropolitan Manila prepares for the 'Big One,' focusing on information
dissemination as to what must be done when the earthquake happens. In order to make a quick
and safe evacuation, it is necessary to formulate a clear-cut evacuation plan, specifically, to create
evacuation routes. In this study, earthquake evacuation was simulated from Philippine General
Hospital (PGH) to Rizal Park to identify optimal evacuation routes quantitatively using genetic
algorithm (GA) and geospatial data. The problem was treated as a multi-objective optimization
problem wherein the evacuation distance was minimized and the arrival probability maximized. Road
networks were mapped using Geographical Information System (GIS) and information on road lengths
and road blockage probability were imported to python. GA was used to search for optimal evacuation
routes. The algorithm yielded a front of Pareto-optimal solutions. Subsequently, analytic hierarchical
process (AHP) was applied to select the best optimal evacuation route according to preference. The
best route identied has a distance of 1089.32 m and an arrival probability of 0.504. The model
contributes to the preparation and planning of evacuation in the event of the 'Big One' ensuring
the safest and most efficient evacuation route.

Strength and fracture analysis of polymer-granular matter composites at variable weight percent ratios

2019-02-04T02:01:38+08:00

In this study, the optimal weight percent ratio of resin and aggregate for a polymer-granular matter composite
(PGMC) was determined in terms of its compressive strength. The PGMC was made with polyester for its
resin, and white sand as its aggregate. The weight percent ratios of the PGMC varied as follows: 15:85, 20:80,
and 25:75 for resin and aggregate respectively. The PGMC specimens underwent a compression test after
a curing period of seven days at room temperature to determine its compression strength. Results indicate
that the PGMC with weight percent ratio 25:75 had the highest average compression strength at 76.4 MPa
which is more than twice the strength of cement-based concrete. The 15:85 and 20:80 PGMCs yielded average
compression strengths of 19.8 MPa and 60.8 MPa respectively. The most common fracture type for the PGMCs
having weight percent ratios 20:80 and 25:75 was shear, occurring 83.3% of the time. On the other hand, the
PGMC having weight percent ratio 15:85 displayed shear wedge fracture for five of the six trials.

A quantum engine by pumping electrons in a nanojunction with a single gate and dynamic tunnel couplings to the leads

2019-02-04T02:01:15+08:00

We configure a source-channel-drain nanojunction to function as either a quantum pump or a quantum engine by dynamically varying the tunnel couplings to the leads and applying a time-dependent gate potential. The dynamics of the time-varying components follow an operating protocal in such a way that electrons are pumped, adiabatically or nonadiabatically, from the left lead, through the channel, and on to the right lead without a source-drain bias potential. We express the electron energy current flowing across the device in terms of nonequilibrium Green’s functions. These nonequilibrium Green’s functions are then expressed in terms of steady-state Green’s functions which are, in turn, expressed in terms of the equilibrium Green’s functions of
the free leads. The equilibrium Green’s functions are determined from the equation of motion of each free lead.

Fluorine-doped SnO₂ thin film as chemiresistive gas sensor for room temperature monitoring of fish freshness

2019-02-04T02:00:58+08:00

Pure and fluorine-doped tin oxide films were prepared using nebulized spray pyrolysis. X-ray diraction (XRD) and scanning electron microscopy (SEM) analyses confirmed the nanocrystalline tetragonal structure of the prepared films. The gas sensing response of the films towards actual fish vapors of varying freshness level was then investigated. Higher sensitivity was observed in the fluorinated tin oxide film compared to the undoped film. Moreover, the degree of the films sensitivity was observed to be proportional to the extent of
the fish spoilage. The results suggest that fluorinated tin oxide can be applied for room temperature monitoring of fish freshness.

Improved linearity, stability, and thermal performance of multi-mesa-channel AlGaN/GaN HEMTs

2019-02-04T02:00:31+08:00

With its wide bandgap of 3.4 eV, gallium nitride (GaN) is considered as a key semiconductor material for realizing ultra-low-loss power devices. However, GaN-based devices is still plagued by current collapse, which is the temporary reduction of current after application of electrical stress. In this work, we present the state-of-art Multi-Mesa-Channel (MMC) AlGaN/GaN HEMT being developed in our laboratory. The MMC HEMT is fabricated in a way to realize parallel mesa-shaped nano-channels separated by trenches. Investigations have revealed that the MMC HEMT is highly resistant to current collapse and other instabilities, making it a leading power electronics prospect.

Paraxial optics cloak using four converging lenses with arbitrary focal lengths

2019-02-04T02:00:18+08:00

In this paper, we achieved cloaking with four converging lenses of any focal length by solving the ray transfer matrix of a four lens optical system. It has been shown before that cloaking can be achieved using four converging lenses (so-called Rochester cloaks) but such cloaks required having 2 sets of 2 lenses with equal focal lengths, which we did not impose. We also discuss how the separation lengths between the lenses are affected by their focal lengths. In addition, we show how our formula holds under Rochester cloak condition.