MedWorm: Physics Top 20

Global stability analysis of birhythmicity in a self-sustained oscillator

Chaos — Wed, 10 Mar 2010 17:59:49 +0100

R. Yamapi, G. Filatrella, and M. A. Aziz-Alaoui We analyze the global stability properties of birhythmicity in a self-sustained system with random excitations. The model is a multi-limit-cycle variation in the van der Pol oscillator introduced to analyze enzymatic substrate reactions in brain waves. We show that the two frequencies are strongly i ... [Chaos 20, 013114 (2010)] published Tue Mar 9, 2010. (Source: Chaos)

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Four probe architecture using high spatial resolution single multi-walled carbon nanotube electrodes for electrophysiology and bioimpedance monitoring of whole tissue

Applied Physics Letters — Thu, 04 Mar 2010 18:17:38 +0100

We report the application of a sensor with a multielectrode architecture consisting of four single multiwalled carbon nanotube electrodes (sMWNT electrodes) with nanotube tip diameters of approximately 30 nm to stimulation, recording, and bioimpedance characterization of whole muscle. Parallel pairs ... [Appl. Phys. Lett. 96, 093701 (2010)] published Wed Mar 3, 2010. (Source: Applied Physics Letters)

Stereotactic Body Radiation Therapy (SBRT) and Respiratory Gating in Lung Cancer: Dosimetric and Radiobiological Considerations.

Journal of Applied Clinical Medical Physics — Fri, 19 Feb 2010 07:54:03 +0100

Authors: De La Fuente Herman T, Vlachaki MT, Herman TS, Hibbitts K, Stoner JA, Ahmad S The purpose of this study was to assess the impact of respiratory gating on tumor and normal tissue dosimetry in patients treated with SBRT for early stage non-small cell lung cancer (NSCLC). Twenty patients with stage I NSCLC were studied. Treatment planning was performed using four-dimensional computed tomography (4DCT) with free breathing (plan I), near end inhalation (plan II) and near end exhalation (plan III). The prescription dose was 60 Gy in 3 fractions. The tumor displacement was most pronounced for lower peripheral lesions (average 7.0 mm, range 4.1-14.3 mm) when compared to upper peripheral (average 2.4 mm, range 1.0-5.1 mm) or central lesions (average 2.9 mm, range 1.0-4.1 mm). There wer...

Opinion: Scientific integrity

Physics Today News Picks — Mon, 14 Dec 2009 00:00:00 +0100

With the public controversy over hacked e-mail messages from climate scientists, scientific integrity has, for some people, put deeply in question. Arguably the fundamental issue boils down to something described in a comment from the late Richard Feynman. He spoke of "a kind of scientific integrity, a principle of scientific thought that corresponds to a kind of utter honesty—a kind of leaning over backwards. For example, if you're doing an experiment, you should report everything that you think might make it invalid—not only what you think is right about it: other causes that could possibly explain your results; and things you thought of that you've eliminated by some other experiment, and how they worked.... Details that could throw doubt on your interpretation must be given, if ...

Exotic heavy antimatter detected at the Relativistic Heavy Ion Collider

Physics Today News Picks — Fri, 05 Mar 2010 00:00:00 +0100

This study of the new antihypernucleus also yields a valuable sample of normal hypernuclei, and has implications for our understanding of the structure of collapsed stars. “The strangeness value could be non-zero in the core of collapsed stars,” said Jinhui Chen, one of the lead authors, a postdoctoral researcher at Kent State University and currently a staff scientist at the Shanghai Institute of Applied Physics, “so the present measurements at RHIC will help us distinguish between models that describe these exotic states of matter.” The findings also pave the way towards exploring violations of fundamental symmetries between matter and antimatter that occurred in the early universe, making possible the very existence of our world. Collisions at RHIC fleetingly produce conditio...

An innovative high-power constant-current pulsed-arc power-supply for a high-density pulsed-arc-plasma ion-source using a LaB-filament

Review of Scientific Instruments — Wed, 24 Feb 2010 17:02:10 +0100

A. Ueno, H. Oguri, K. Ikegami, Y. Namekawa, K. Ohkoshi et al. An innovative high-power constant-current (CC) pulsed-arc (PA) power-supply (PS) indispensable for a high-density PA plasma ion-source using a lanthanum hexaboride (LaB) filament was devised by combining a constant-voltage (CV) PA-PS, which is composed of an insulated gate bipolar transistor (IGBT) ... [Rev. Sci. Instrum. 81, 02A718 (2010)] published Mon Feb 22, 2010. (Source: Review of Scientific Instruments)

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Death of a deep-sea robot

Physics Today News Picks — Tue, 09 Mar 2010 00:00:00 +0100

Physics Today: A pioneering deep-sea exploration robot—one of the first successful submersible vehicles that was both unmanned and untethered to surface ships—was lost at sea on a research expedition to explore the Chile Triple Junction—the only place on Earth where a mid-ocean ridge is being subducted (or pushed) beneath a continent (South America) in a deep ocean trench. The 15-year-old Autonomous Benthic Explorer (ABE), was launched late Thursday night by the Woods Hole Oceanographic Institution (WHOI) and had reached the seafloor to begin its 222nd research dive when, in the early hours of Friday morning, all contact with the surface vessel Melville abruptly ceased. All efforts to reestablish contact failed. “The loss had nothing to do with earthquake activity off...

Polymer:metal nanoparticle devices with electrode-sensitive bipolar resistive switchings and their application as nonvolatile memory devices

Applied Physics Letters — Sat, 13 Feb 2010 16:13:53 +0100

Jianyong Ouyang and Yang Yang Devices with a polystyrene film blended with gold nanoparticles capped with conjugated 2-naphthalenethiol exhibited electrode-sensitive bipolar resistive switchings. The resistances of the two states could be different by almost three orders of magnitude, and the devices could be switched between th ... [Appl. Phys. Lett. 96, 063506 (2010)] published Fri Feb 12, 2010. (Source: Applied Physics Letters)

A two-stage sequential linear programming approach to IMRT dose optimization.

Physics in Medicine and Biology — Sat, 16 Jan 2010 17:12:30 +0100

Authors: Zhang HH, Meyer RR, Wu J, Naqvi SA, Shi L, D'Souza WD The conventional IMRT planning process involves two stages in which the first stage consists of fast but approximate idealized pencil beam dose calculations and dose optimization and the second stage consists of discretization of the intensity maps followed by intensity map segmentation and a more accurate final dose calculation corresponding to physical beam apertures. Consequently, there can be differences between the presumed dose distribution corresponding to pencil beam calculations and optimization and a more accurately computed dose distribution corresponding to beam segments that takes into account collimator-specific effects. IMRT optimization is computationally expensive and has therefore led to the use of heurist...

Concerning the health effects of internally deposited radionuclides.

Health Physics — Sat, 13 Feb 2010 16:52:23 +0100

Authors: Raabe OG The ionizing radiation dose-response relationships for internally deposited radionuclides are examined using data from humans involving Ra and laboratory animal studies involving alpha-emitters Ra, Ra, Ra, Th, Pu, Pu, and Am and beta-emitters Y, Sr, Y, and Ce. Intake routes included ingestion, inhalation, and injection. The lifetime effects are best described by three-dimensional average-dose-rate/time/response surfaces that compete with other causes of death during an individual's lifetime. Using maximum likelihood survival regression methods, the characteristic logarithmic slope for cancer induction was found to be about negative one-third for alpha-emitters or about negative two-thirds for beta-emitters. At the higher average dose-rates the principal deleterious ef...

The treatment of solid tumors by alpha emitters released from (224)Ra-loaded sources-internal dosimetry analysis.

Physics in Medicine and Biology — Sat, 06 Feb 2010 05:46:05 +0100

Authors: Arazi L, Cooks T, Schmidt M, Keisari Y, Kelson I Diffusing alpha-emitters radiation therapy (DART) is a proposed new form of brachytherapy, allowing the treatment of solid tumors by alpha particles. DART utilizes implantable sources carrying small activities of radium-224, which continually release into the tumor radon-220, polonium-216 and lead-212 atoms, while radium-224 itself remains fixed to the source. The released atoms disperse inside the tumor by diffusive and convective processes, creating, through their alpha emissions, a high-dose region measuring several mm in diameter about each source. The efficacy of DART has been demonstrated in preclinical studies on mice-borne squamous cell carcinoma and lung tumors and the method is now being developed toward clinical trial...

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Machine vision for digital microfluidics

Review of Scientific Instruments — Sat, 23 Jan 2010 16:02:05 +0100

Yong-Jun Shin and Jeong-Bong Lee Machine vision is widely used in an industrial environment today. It can perform various tasks, such as inspecting and controlling production processes, that may require humanlike intelligence. The importance of imaging technology for biological research or medical diagnosis is greater than ever. Fo ... [Rev. Sci. Instrum. 81, 014302 (2010)] published Fri Jan 22, 2010. (Source: Review of Scientific Instruments)

The utility of non-axial treatment beam orientations for lower lobe lung cancers.

Journal of Applied Clinical Medical Physics — Fri, 19 Feb 2010 07:54:03 +0100

Conclusion: Non-axial beams can reduce the dose to the heart and liver in patients with lower lobe lung cancers. Non-axial beams may be clinically beneficial in these patients and should be considered as an option during planning. PMID: 20160689 [PubMed - in process] (Source: Journal of Applied Clinical Medical Physics)

Ferrimagnetism in zigzag graphene nanoribbons induced by main-group adatoms

Applied Physics Letters — Tue, 09 Mar 2010 17:12:06 +0100

Erjun Kan, Hongjun Xiang, Fang Wu, Changhoon Lee, Jinlong Yang et al. Density functional calculations for zigzag graphene nanoribbons (ZGNRs) with adsorbed adatom A (=B,C,N) show that these adatoms prefer the sites near the edge, and convert the antiferromagnetism of pristine ZGNRs into ferrimagnetism with high magnetic moment (i.e., 1, 2, and 1 [mu] per adatom for A ... [Appl. Phys. Lett. 96, 102503 (2010)] published Mon Mar 8, 2010. (Source: Applied Physics Letters)

Defect annealing in neutron and ion damaged silicon: Influence of defect clusters and doping

Journal of Applied Physics — Sat, 06 Mar 2010 16:15:24 +0100

R. M. Fleming, C. H. Seager, E. Bielejec, G. Vizkelethy, D. V. Lang et al. We have explored defect annealing in radiation damaged silicon in a regime characterized by defect clusters and higher doping. Several types of pnp and npn Si bipolar transistors have been irradiated with ions and neutrons, then isochronally annealed from 300 to 600 K to study the evolution of deep ... [J. Appl. Phys. 107, 053712 (2010)] published Fri Mar 5, 2010. (Source: Journal of Applied Physics)

Geometric constrains for detecting short actin filaments by cryogenic electron tomography

PMC Biophysics — Fri, 05 Mar 2010 00:00:00 +0100

Polymerization of actin into filaments can push membranes forming extensions like filopodia or lamellipodia, which are important during processes such as cell motility and phagocytosis. Similarly, small organelles or pathogens can be moved by actin polymerization. Such actin filaments can be arranged in different patterns and are usually hundreds of nanometers in length as revealed by various electron microscopy approaches. Much shorter actin filaments are involved in the motility of apicomplexan parasites. However, these short filaments have to date not been visualized in intact cells. Here, we investigated Plasmodium sporozoites, the motile forms of the malaria parasite that are transmitted by the mosquito, using cryogenic electron tomography. We detected filopodia-like extensions of the...

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Gold nanorods as new nanochromophores for photothermal therapies

Journal of Biophotonics — Mon, 01 Mar 2010 00:00:00 +0100

Results and perspectives on the biomedical exploitation of gold nanorods with plasmon resonances in the near infrared window are reported. The authors describe experimental studies of laser-activated nanoparticles in the direct welding of connective tissues, which may become a valuable technology in biomedicine. In particular, colloidal gold nanorods excited by diode laser radiation at 810 nm were used to mediate functional photothermal effects and weld eye's lens capsules and arteries. The preparation of biopolymeric matrices including gold nanorods is also described, as well as preliminary tests for their application in the closure of wounds in vessels and tendons. Finally, the use of these nanoparticles for future applications in the diagnosis, imaging and therapy of cancer is discussed...

High electron mobility in bipolar composites of organic molecules

Applied Physics Letters — Mon, 22 Feb 2010 16:53:35 +0100

L.-B. Lin, S. A. Jenekhe, and P. M. Borsenberger Electron and hole mobilities in bipolar molecular composites of N,N[prime]-bis(1,2-dimethyl- propyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NTDI) and tri-p-tolylamine (TTA) are reported. The electron mobility in NTDI/TTA composites is found to be enhanced by factors of 4 to 6 compared to pure N ... [Appl. Phys. Lett. 69, 3495 (2010)] published Mon Feb 22, 2010. (Source: Applied Physics Letters)

Free Energy Profile of RNA Hairpins: A Molecular Dynamics Simulation Study.

Biophysical Journal — Wed, 17 Feb 2010 00:00:00 +0100

In this study, the calculations using AMBER force field give a qualitatively correct description for the folding of two RNA hairpins, as the calculated PMF confirms the global stability of the folded structures and the resulting relative folding free energy is in quantitative agreement with the experimental result. The hairpin stabilities are also correctly differentiated by the more rapid molecular mechanics-Poisson Boltzmann-surface area approach, but the relative free energy estimated from this method is overestimated. The free energy profile shows that the native state basin and the unfolded state plateau are separated by a wide shoulder region, which samples a variety of native-like structures with frayed terminal basepair. The calculated PMF lacks major barriers that are expected nea...

Partitioning of Nonsteroidal Antiinflammatory Drugs in Lipid Membranes: A Molecular Dynamics Simulation Study.

Biophysical Journal — Wed, 17 Feb 2010 00:00:00 +0100

Authors: Boggara MB, Krishnamoorti R Using the potential of mean constrained force method, molecular dynamics simulations with atomistic details were performed to examine the partitioning and nature of interactions of two nonsteroidal antiinflammatory drugs, namely aspirin and ibuprofen, in bilayers of dipalmitoylphosphatidylcholine. Two charge states (neutral and anionic) of the drugs were simulated to understand the effect of protonation or pH on drug partitioning. Both drugs, irrespective of their charge state, were found to have high partition coefficients in the lipid bilayer from water. However, the values and trends of the free energy change and the location of the minima in the bilayer are seen to be influenced by the drug structure and charge state. In the context of the trans...