Collisions between carbon dioxide molecules can affect greenhouse warming.

By Physics Today on July 3, 2008 11:37 AM |

Visible light coming from the Sun pours down daily and is reflected back from Earth's surface as IR radiation. Extra warming occurs when some of that IR is absorbed and retained in the atmosphere. Only a trace gas in the atmosphere, CO2 is far outnumbered by O2 and N2 molecules, but its growing presence (mostly due to human activity) and its ability to absorb and trap IR radiation are thought to be instrumental in producing greenhouse effects. The interactions between atoms in a single molecule generate the molecule's dipole moment and polarizability, two properties that greatly affect how the molecule absorbs or scatters radiation. Going to the next level of complexity, a new study shows in detail how a large class of molecules, including CO2, absorbs and sometimes scatters light energy during intermolecular collisions. Michael Chrysos and his colleagues at the University of Angers (France) and Saint Petersburg State University (Russia) have derived exact mathematical formulas that can be used to calculate how collisions between so-called linear-rotor molecules modify the molecules' absorption spectra. During a molecular interaction, a transient supermolecular complex arises with its own degrees of freedom—distinct from those of the constituent molecules—and its own dipole moment or polarizability. The net result is that a broad band of frequencies, including many that are unavailable to single molecules, can be absorbed or scattered. The new study is important for several reasons: It allows exact calculations of how the intercepted IR photon energy is converted to kinetic energy and shared among neighboring gas molecules; it allows for the inclusion of higher-order effects, such as the simultaneous collision of three molecules; and it provides evidence that long-range intermolecular interactions are far more important than short-range ones for absorption, a conclusion in conflict with mainstream assumptions. (M. Chrysos et al., Phys. Rev. Lett. 100, 133007, 2008 [SPIN].) — Phillip F. Schewe

A natural quasicrystal

By Physics Today on June 22, 2009 10:28 AM |

The hallmark of a conventional crystal such as table salt is translational symmetry. Quasicrystals do not have that symmetry and so can exhibit a wider structural variety than their more constrained brethren. But quasicrystals, like crystals, do have long-range correlations and display sharp, structure-revealing diffraction patterns. To date, more than 100 quasicrystals have been synthesized in the lab. Now Luca Bindi of the Natural History Museum of Florence has teamed up with Paul Steinhardt and colleagues from Princeton and Harvard universities to present evidence for a natural version of one of those quasicrystals: icosahedral Al₆₃Cu₂₄Fe₁₃. The material, a 100-μm grain, is from a mineral assemblage (left figure) excavated from the Koryak Mountains in Russia and now housed in the Florence museum; the very complexity of the sample argues for its natural formation. In consultation with his US-based colleagues, Bindi identified the sample as possibly hosting a quasicrystal. The US team then probed a small piece of it with transmission electron microscopy. Diffraction patterns such as shown in the right figure identified quasicrystal regions; the 10-fold symmetry cannot be generated by crystals. Subsequent analysis of x rays scattered off pure quasicrystal grains determined the material’s chemical formula. Geologists and physicists have much to learn about the conditions under which quasicrystals form. The study of natural materials can help address that question and may turn up new, never-before contemplated structures. (L. Bindi et al., Science 324, 1306, 2009.) —Steven K. Blau

Physics of Ferroelectric

Physics of Ferroelectric

Publish at Scribd or explore others: Academic Work Religion & Spiritual Science-Physics

Nanotube loudspeakers

Physics Today , 2008

In typical loudspeakers, a coil surrounds the apex of a flexible cone; when a varying current flows through the coil, the cone moves toward and away from a fixed permanent magnet and produces pressure waves we hear as sound. But researchers from Tsinghua University and Beijing Normal University have demonstrated a radically simpler loudspeaker design based on nanotubes: They showed that a thin film of nanotubes can reproduce sounds over a wide frequency range--including the full human audible range--with high sound pressure level, low total harmonic distortion, and no magnets. The team created the film by drawing nanotubes from a so-called superaligned array grown on a wafer, a technique the group introduced six years ago (see also PHYSICS TODAY, October 2005, page 23). The resulting film, only tens of nanometers thick but up to 10 cm wide, is transparent and has a nearly purely resistive impedance. When electrodes are placed along its ends and an alternating current is applied, the film produces clear tones that can be as loud as a conventional speaker. Moreover, since the film is flexible, the nanotube speaker can be configured into arbitrary shapes or mounted onto curved substrates; the figure shows an omnidirectional cylindrical loudspeaker 9 cm in diameter and 8.5 cm high. The film can even be stretched with essentially no degradation of the sound reproduction. The researchers attribute the sound generation not to vibration but to a thermoacoustic effect first proposed nearly a century ago: Thanks to the nanotube film's extremely low heat capacity per unit area, changes in the current flowing through the film are reflected in the film's temperature, and those temperature changes excite pressure waves in the surrounding air. The mechanism is independent of the sign of the current, which leads to a frequency doubling of the input signal, but that drawback can be overcome by applying a constant current bias. The movie shows a nanotube loudspeaker being periodically stretched with almost no noticeable effect on the sound intensity. (L. Xiao et al., Nano Lett., in press, doi:10.1021/nl802750z.) -- Richard J. Fitzgerald

2009 IEEE International Ultrasonics Symposium

Short Courses & Tutorials

September 20-23, 2009

Ergife Palace Hotel, Roma, Italy

Sponsored by the IEEE Ultrasonics, Ferroelectrics, & Frequency Control Society

In the section Symposium/Announcements, we have published the Second Call for Papers of 2009 IUS - Roma. Please, download and print the pdf-file with Adobe Acrobat and show it in your Institution
Second Call for Papers
Abstract Deadline: May 3, 2009

We are pleased to welcome you to the 2009 IEEE International Ultrasonics Symposium, which
will be held in Roma, Italy, from September 20 to 23 at the Ergife Palace Hotel.
We are sure that you will enjoy your visit to Roma, which is rightly known as one of the most
beautiful and interesting cities in the world. It is the city of the Caesars with majestic
monuments from the golden days of the ancient Roman Empire. But it is also the center of
the catholic world, with an endless number of grand, beautiful cathedrals and churches. But
Roma is so much more than an open-air museum; everywhere you find great restaurants with
superb food and wine, lovely bars and cafés, excellent shopping, and vibrant night life.
We look forward to meeting you in Roma.
Papers are solicited for this conference describing original work in the field of ultrasonics.
Poster and oral presentation formats will be used at the symposium. Prospective authors
should note that poster sessions provide an alternative format which allows for greater
flexibility and expanded audience interaction. The deadline for submission of abstracts is May
3, 2009. The abstracts should be submitted in electronic form according to the specific
information posted on the conference web page. Additional conference information can be
found at the Symposium web site: http://ewh.ieee.org/conf/ius_2009/. Each abstract will
receive careful review and evaluation by the Symposium Technical Program Committee.
Evaluation criteria will include originality of the work, contribution to the state-of-the-art, and
overall interest to the ultrasonics community. Papers are solicited from the following subject
classifications:

Group 1 : Medical Ultrasonics
MBB Medical Beamforming and Beam Steering
MBE Biological Effects & Dosimetry
MBF Blood Flow Measurement
MCA Contrast Agents
MEL Elastography
MIM Medical Imaging
MPA Medical Photoacoustics
MSD System & Device Design
MSP Medical Signal Processing
MTC Medical Tissue Characterization
MTH Therapeutics, Hyperthermia, and Surgery
Group 3: Physical Acoustics
PBW Bulk Wave Effects & Devices
PGP General Physical Acoustics
PLP Physical Acoustics Laser Interactions
PMI Magnetic/Electromagnetic Interactions
POI Optical Interactions
PPN Phononic Crystals & Devices
PUM Ultrasonic Motors & Actuators
PTF Thin Films
Group 5: Transducers & Transducer Materials
TMC Materials Characterization and Fabrication
TPF Ultrasonic Applications of Piezoelectrics &
Ferroelectrics
TMI Medical Imaging Transducers
TMO Modeling (Analytical & Numerical)
TMU Micromachined Ultrasound Transducers
TTT Medical Therapeutic Transducers
TFT Thick Film Piezo-Technology
Group 2: Sensors, NDE & Industrial Applications
NAM Acoustic Microscopy
NAI Acoustic Imaging
NAS Acoustic Sensors
NDE General NDE Methods
NFM Flow Measurement
NMC Material & Defect Characterization
NSP Signal Processing
NTD Transducers: NDE and Industrial
NWP Wave Propagation
Student Travel Support: Limited funds are available to support IEEE UFFC student member attendees at the 2009 symposium. Awards will be given on a competitive basis. Please see the conference website for details.
Student Paper Competition: Students submitting abstracts are invited to participate in a student paper competition. To participate, the student must be the lead author and present his/her paper. Further information will be posted on the conference website (http://ewh.ieee.org/conf/ius_2009/)
All roads lead to Rome ...

http://ewh.ieee.org/conf/ius_2009

Unified Model or Feroics Hysterisis

Unified Theory for Hysterisis Model

Publish at Scribd or explore others: hysterisis ferroelectric

TEORI DOMAIN WALL untuk Material Ferreoelektrik

Teguh Yoga Raksa ( 2008)

Model histerisis dari ferroelektrik material dapat dikelompokan menjadi beberapa kategori, salah satu kategorinya adalah teori mikroskopis material yang mengacu pada proses pembalikan domain, mekanisme pergerakan dinding domain akibat adanya pengaruh medan listrik dari luar. Sifat dielektrik dari material ferroelektrik dapat dijadikan acuan untuk pemodelan dengan menggunakan statistik boltzman untuk menghitung probabilitas dipol yang menempati energi level tertentu. Beberapa pemodelan yang mengacu pada fenomena domain akan diperkenalkan, yaitu pemodelan dengan menggunakan perumusan Langevin, model Ising Spin dan model yang ketiga adalah gabungan dari keduanya .

Pemodelan pada umumnya menggambarkan adanya area padat dimana perputaran dipol berlawanan arah dengan konfigurasi ionik sehingga menyebabkan perubahan yang sangat besar pada polarisasinya, dan hal ini memperlihatkan adanya saturasi pada saat level medan tinggi ketika distribusi muatan tidak diperkenankan untuk perubahan selanjutnya. Sebaliknya pengukuran kurva polarisasi pada saat level yang tinggi anhysterisis memikili nilai tunggal dan reversibel. Medan efektif dengan asumsi ideal dapat diformulasikan seperti persamaan berikut :

Ee =E+alpha*P

Besaran E, P menunjukan medan listrik dan hasil polarisasi sementara nilai aP merupakan menunjukan interdomain kopling. Pendekatan statistik Boltzman digunakan untuk menghitung probabilitas dipol – dipol yang menempati energi keadaan tertentu, dengan asumsi material isotropik , orientasi sel ke segala arah dan dicapainya keseimbangan termal dan elektrostatik maka diperoleh persamaan Langevin untuk polarisasi anhisterisis.

Model yang kedua pada polarisasi anhisterisis adalah model Ising Spin, dimana mengasumsikan bahwa orientasi momen dipol hanya pada arah medan listrik atau berlawanan arah .

Model yang ketiga adalah model gabungan dari model Langevin dan Ising Spin, model ini dibuat dengan asumsi grain pada material terdistribusi secara acak, akan tetapi dipol – dipol setiap sel hanya memiliki dua arah orientasi yang mungkin, ketiga model ini dapat dpergunakan untuk menghitung polarisasi anhysteritic akibat adanya medan listrik luar

referensi :

Ralph C Smith dan Craig L. Hom, A domain Wall Theory for Ferrolectric Material , Jurnal of Intelligent Material Systems and Structures, 1999