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BIOTEKNOLOGI DALAM PEMBANGUNAN PERTANIAN
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| Pengarang | : | K.H. Timotius |
| Nama Majalah/Jurnal | : | Bina Darma |
| Volume / Edisi | : | 5-17 (No. 17) |
| Halaman | : | 15-24 |
| Abstrak | : | - |
The harmonic quantum Szilárd engine
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 12) |
| Halaman | : | 1123-1131 |
| Abstrak | : | The Szilárd engine is a mechanism (akin to Maxwell's demon) for converting information into energy, which seemingly violates the second law of thermodynamics. Originally a classical thought experiment, it was extended to a quantized treatment by Zurek. Here, we examine a new, elegant model of a quantum Szilárd engine by replacing the traditional rigid box with a harmonic potential, extending the scope of the model. Remarkably, almost all calculations are exact. This article is suitable for students, researchers, and educators interested in the conceptual links among information, entropy, and quantum measurement. |
Classical and quantum confocal parabolic billiards
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 12) |
| Halaman | : | 1113-1122 |
| Abstrak | : | The classical and quantum description of a free particle moving inside a confocal parabolic billiard is studied. From a classical approach, we derive the characteristic equations for periodic trajectories, discuss the Poincaré maps, and explore interesting geometrical properties of the orbits inside the billiard. From a quantum description, we determine the eigenstates and energy spectrum of the confined particle. The confocal parabolic billiard is an integrable system that exhibits two degrees of freedom and two constants of motion. The way to establish a correspondence between the classical and quantum solutions is by equating the constants of motion for both descriptions. The parabolic billiard provides a well-motivated and relatively straightforward example of the Hamilton–Jacobi theory in a way that is seldom discussed in the undergraduate curriculum. |
REVOLUSI HIJAU
| Pengarang | : | Rukmadi Warsito |
| Nama Majalah/Jurnal | : | Bina Darma |
| Volume / Edisi | : | 5-17 (No. 17) |
| Halaman | : | 6-14 |
| Abstrak | : | - |
An exact solution for a particle in a velocity-dependent force field
| Pengarang | : | David Laroze |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 12) |
| Halaman | : | 1103-1112 |
| Abstrak | : | We revisit the classical mechanics problem of a particle moving under the influence of a force that depends on its velocity. Using the properties of the rotation matrix and associated operators, we show that it is possible to find an exact analytical solution to a number of problems where the differential equation of motion depends on the velocity. First, we apply our method to the well-known cases of a particle under the influence of the Lorentz force and Coriolis force, providing the complete analytical solution in each case for the motion of the particle in three dimensions. We also show that the complete solution can be obtained when the centrifugal force is included, showing the applicability to cases where there is simultaneous dependence on the position and velocity. This method, which is not currently discussed in a typical course in elementary mechanics, provides an alternative approach to the traditional methods that are used to solve these types of problems. |
On the ubiquity of classical harmonic oscillators and a universal equation for the natural frequency of a perturbed system
| Pengarang | : | J. J. Bissell |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 12) |
| Halaman | : | 1094-1102 |
| Abstrak | : | A new perspective on the ubiquity of classical harmonic oscillators is presented based on the two-variable Taylor expansion of a perturbed system's total energy ?, where q(t) is the system displacement as a function of time t and ?. This generalised approach permits derivation of the lossless oscillator equation from energy arguments only, yielding a universal equation for the oscillation frequency which may be applied to arbitrary systems without the need to form system-specific linearised models. As illustrated by a range of examples, this perspective gives a unifying explanation for the prevalence of harmonic oscillators in classical physics, can be extended to include damping effects and driving forces, and is a powerful tool for simplifying the analyses of perturbed systems. |
Measuring the balance of the world's largest machine
| Pengarang | : | William H. Baird |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 12) |
| Halaman | : | 1086-1093 |
| Abstrak | : | The electrical power grid has been described as the largest machine in the world. Although we customarily assume our electrical outlets provide a steady sinusoidal voltage with a frequency of 60 Hz (in North America), the variations from that ideal are easy to observe using the methods described in this article. These frequency variations are important since, as can be shown with introductory-level physics concepts, they arise when power generation and usage are not balanced on the electrical grid. The challenge of balancing the electrical grid will increase over the coming years as we adopt more sustainable but less predictable energy sources, and this connection to one of our current societal challenges makes this project interesting to students. |
Slings and Spirals
| Pengarang | : | Michael B. Soebagyo |
| Nama Majalah/Jurnal | : | Siam News |
| Volume / Edisi | : | 58 (No. 3) |
| Halaman | : | 7 |
| Abstrak | : | Spirals whose curvatures are exponential functions of the arclength are denser near their centers than logarithmic spirals (see Figure 1). I stumbled upon these exponential spirals thanks to an inspiring conversation with mathematician Tadashi Tokieda. |
Using smartphone photographs of the Moon to acquaint students with non-Euclidean geometry
| Pengarang | : | Kin Son Wong |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 12) |
| Halaman | : | 1079-1085 |
| Abstrak | : | Non-Euclidean geometry can be taught to students using astronomical images. By using photographs of the Moon taken with a smartphone through a simple telescope, we were able to introduce these concepts to high-school students and lower-level college students. We teach students how to calculate lengths of mountain ranges or areas of craters on the Moon's surface and introduce ideas of geodesics and spherical triangles. Students can see that accurate measurements cannot be obtained using flat geometry. Instead, by using three-dimensional curved geometry, estimates of lengths and areas can be computed with less than 4% error. |
The Fiction Machine
| Pengarang | : | Leon Bottou Bernhard Scholkopf |
| Nama Majalah/Jurnal | : | Siam News |
| Volume / Edisi | : | 58 (No. 3) |
| Halaman | : | 3-4 |
| Abstrak | : | Today’s computers can talk back to us. This fact alone is momentous enough, but humans are a greedy kind. If computers talk, then they must think. If they think, then they must be intelligent — like artificial intelligences in the movies. The scene is loud with businessmen hyping their technologies, ideologues pushing their creeds, and industrialists placing their bets. |