Thomson microwave scattering for diagnostics of small plasma objects enclosed within glass tubes.

In this work, coherent microwave scattering in the Thomson regime was demonstrated for small-scale plasmas enclosed within a glass tube and validated using a well-known hairpin resonator probe technique. The experiments were conducted in a DC discharge tube with a diameter of 1.5 cm and a length of 7 cm. Thomson microwave scattering (TMS) diagnostics yielded electron number densities of about 5.9 × 1010 cm-3, 2.8 × 1010 cm-3, and 1.8 × 1010 cm-3 for air pressures in the discharge tube of 0.2, 0.5, and 2.5 Torr, respectively. Measurements using the TMS technique were consistent across the tested microwave frequencies of 3-3.9 GHz within the margin of error associated with non-idealities of the IQ mixer utilized in the circuit. The corresponding densities measured with the hairpin resonator probe were 4.8 × 1010, 3.8 × 1010, and 2.6 × 1010 cm-3. Discrepancies between the two techniques were within 30% and can be attributed to inaccuracies in the sheath thickness estimation required for correct interpretation of the hairpin resonator probe results.

Ionization rate and plasma dynamics at 3.9 micron femtosecond photoionization of air.

The introduction of mid-IR optical parametric chirped pulse amplifiers has catalyzed interest in multimillijoule, infrared femtosecond pulse-based filamentation. As tunneling ionization is a fundamental first stage in these high-intensity laser-matter interactions, characterizing the process is critical to understand derivative topical studies on femtosecond filamentation and self-focusing. Here, we report direct nonintrusive measurements of total electron count and electron number densities generated at 3.9 µm femtosecond midinfrared tunneling ionization of atmospheric air using constructive-elastic microwave scattering. Subsequently, we determine photoionization rates to be in the range 5.0×10^{8}-6.1×10^{9}s^{-1} for radiation intensities of 1.3×10^{13}-1.9×10^{14}W/cm^{2}, respectively. The proposed approach paves the wave to precisely tabulate photoionization rates in mid-IR for a broad range of intensities and gas types and to study plasma dynamics at mid-IR filamentation.

Thomson and collisional regimes of in-phase coherent microwave scattering off gaseous microplasmas.

The total number of electrons in a classical microplasma can be non-intrusively measured through elastic in-phase coherent microwave scattering (CMS). Here, we establish a theoretical basis for the CMS diagnostic technique with an emphasis on Thomson and collisional scattering in short, thin unmagnetized plasma media. Experimental validation of the diagnostic is subsequently performed via linearly polarized, variable frequency (10.5-12 GHz) microwave scattering off laser induced 1-760 Torr air-based microplasmas (287.5 nm O2 resonant photoionization by ~ 5 ns, < 3 mJ pulses) with diverse ionization and collisional features. Namely, conducted studies include a verification of short-dipole-like radiation behavior, plasma volume imaging via ICCD photography, and measurements of relative phases, total scattering cross-sections, and total number of electrons [Formula: see text] in the generated plasma filaments following absolute calibration using a dielectric scattering sample. Findings of the paper suggest an ideality of CMS in the Thomson "free-electron" regime-where a detailed knowledge of plasma and collisional properties (which are often difficult to accurately characterize due to the potential influence of inhomogeneities, local temperatures and densities, present species, and so on) is unnecessary to extract [Formula: see text] from the scattered signal. The Thomson scattering regime of microwaves is further experimentally verified via measurements of the relative phase between the incident electric field and electron displacement.

Erratum: Electric discharge during electrosurgery.

This corrects the article DOI: 10.1038/srep09946.

Enhancing cold atmospheric plasma treatment of cancer cells by static magnetic field.

It has been reported since late 1970 that magnetic field interacts strongly with biological systems. Cold atmospheric plasma (CAP) has also been widely studied over the past few decades in physics, biology, and medicine. In this study, we propose a novel idea to combine static magnetic field (SMF) with CAP as a tool for cancer therapy. Breast cancer cells and wild type fibroblasts were cultured in 96-well plates and treated by CAP with or without SMF. Breast cancer cells MDA-MB-231 showed a significant decrease in viability after direct plasma treatment with SMF (compared to only plasma treatment). In addition, cancer cells treated by the CAP-SMF-activated medium (indirect treatment) also showed viability decrease but was slightly weaker than the direct plasma-SMF treatment. By integrating the use of SMF and CAP, we were able to discover their advantages that have yet to be utilized. Bioelectromagnetics. 38:53-62, 2017. © 2016 Wiley Periodicals, Inc.

Electric discharge during electrosurgery.

Electric discharge utilized for electrosurgery is studied by means of a recently developed method for the diagnostics of small-size atmospheric plasma objects based on Rayleigh scattering of microwaves on the plasma volume. Evolution of the plasma parameters in the near-electrode sheaths and in the positive column is measured and analyzed. It is found that the electrosurgical system produces a glow discharge of alternating current with strongly contracted positive column with current densities reaching 10(3) A/cm(2). The plasma electron density and electrical conductivities in the channel were found be 10(16) cm(-3) and (1-2) Ohm(-1) cm(-1), respectively. The discharge interrupts every instance when the discharge-driving AC voltage crosses zero and re-ignites again every next half-wave at the moment when the instant voltage exceeds the breakdown threshold.

Cold atmospheric plasma for the ablative treatment of neuroblastoma.

BACKGROUND: Recent breakthroughs have allowed for production of plasma at room temperature. Cold atmospheric plasma (CAP) may offer the capability of delivering reactive oxygen species directly into tissues, representing a novel modality for targeted cancer therapy. We studied helium-based CAP's effect on neuroblastoma, both in-vitro and in an in-vivo murine model. METHODS: Mouse neuroblastoma cultures were treated with CAP for 0, 30, 60, and 120 s and assayed for apoptotic and metabolic activity immediately and at 24 and 48 h post-treatment. Five-millimeter tumors were ablated with a single transdermal CAP treatment, and tumor volume and mouse survival were measured. RESULTS: CAP decreased metabolic activity, induced apoptosis, and reduced viability of cancer cells in proportion to both duration of exposure and time post-treatment. In-vivo, a single treatment ablated tumors and eventual tumor growth was decelerated. Furthermore, survival nearly doubled, with median survival of 15 vs. 28 days (p<0.001). CONCLUSIONS: Our findings demonstrate the sensitivity of neuroblastoma to CAP treatment, both in-vitro and in an in-vivo mouse model of established tumor. While further investigation is necessary to establish the mechanism and optimize the treatment protocol, these initial observations establish cold atmospheric plasma as a potentially useful ablative therapy in neuroblastoma.

Simultaneous synthesis of single-walled carbon nanotubes and graphene in a magnetically-enhanced arc plasma.

Carbon nanostructures such as single-walled carbon nanotubes (SWCNT) and graphene attract a deluge of interest of scholars nowadays due to their very promising application for molecular sensors, field effect transistor and super thin and flexible electronic devices(1-4). Anodic arc discharge supported by the erosion of the anode material is one of the most practical and efficient methods, which can provide specific non-equilibrium processes and a high influx of carbon material to the developing structures at relatively higher temperature, and consequently the as-synthesized products have few structural defects and better crystallinity. To further improve the controllability and flexibility of the synthesis of carbon nanostructures in arc discharge, magnetic fields can be applied during the synthesis process according to the strong magnetic responses of arc plasmas. It was demonstrated that the magnetically-enhanced arc discharge can increase the average length of SWCNT (5), narrow the diameter distribution of metallic catalyst particles and carbon nanotubes (6), and change the ratio of metallic and semiconducting carbon nanotubes (7), as well as lead to graphene synthesis (8). Furthermore, it is worthwhile to remark that when we introduce a non-uniform magnetic field with the component normal to the current in arc, the Lorentz force along the J×B direction can generate the plasmas jet and make effective delivery of carbon ion particles and heat flux to samples. As a result, large-scale graphene flakes and high-purity single-walled carbon nanotubes were simultaneously generated by such new magnetically-enhanced anodic arc method. Arc imaging, scanning electron microscope (SEM), transmission electron microscope (TEM) and Raman spectroscopy were employed to analyze the characterization of carbon nanostructures. These findings indicate a wide spectrum of opportunities to manipulate with the properties of nanostructures produced in plasmas by means of controlling the arc conditions.

Controlling diameter distribution of catalyst nanoparticles in arc discharge.

It is demonstrated that the diameter distribution of catalyst nanoparticles in arc discharge can be controlled by a magnetic field. The magnetic field affects the arc shape, shortens the diffusing time of the catalyst nanoparticles through the nucleation zone, and consequentially reduces the average diameters of nanoparticles. The average diameter is reduced from about 7.5 nm without magnetic field to about 5 nm is the case of a magnetic field. Decrease of the catalyst nanoparticle diameter with magnetic field correlates well with decrease in the single-wall carbon nanotube and their bundles diameters.

Tailored distribution of single-wall carbon nanotubes from arc plasma synthesis using magnetic fields.

We report a method for tuning the distribution of single-wall carbon nanotubes (SWCNTs) produced by the anodic arc production method via the application of nonuniform magnetic fields to the gap region during synthesis. Raman, ultraviolet-visible-near-infrared absorbance and near-infrared fluorescence spectroscopies were used to characterize samples together with scanning electron microscopy. Application of the nonuniform magnetic field 0.2-2 kG results in a broadening of the diameter range of SWCNTs produced toward decreased diameters, with substantial fractions of produced SWCNTs being of small diameter, less than ∼1.3 nm, at the highest field. The ability to tune production of the arc production method may allow for improvement in achievable SWCNT properties.

Syndecan-1 regulates cell migration and fibronectin fibril assembly.

Corneal scarring is a major cause of blindness worldwide and can result from the deposition of abnormal amounts of collagen fibers lacking the correct size and spacing required to produce a clear cornea. Collagen fiber formation requires a preformed fibronectin (FN) matrix. We demonstrate that the loss of syndecan1 (sdc1) in corneal stromal cells (CSC) impacts cell migration rates, the sizes and composition of focal and fibrillar adhesions, the activation of integrins, and the assembly of fibronectin into fibrils. Integrin and fibronectin expression are not altered on sdc1-null CSCs. Cell adhesion, spreading, and migration studies using low compared to high concentrations of FN and collagen I (CNI) or vitronectin (VN) with and without activation of integrins by manganese chloride show that the impact of sdc1 depletion on integrin activation varies depending on the integrin-mediated activity evaluated. Differences in FN fibrillogenesis and migration in sdc1-null CSCs are reversed by addition of manganese chloride but cell spreading differences remain. To determine if our findings on sdc1 were specific to the cornea, we compared the phenotypes of sdc1-null dermal fibroblasts with those of CSCs. We found that without sdc1, both cell types migrate faster; however, cell-type-specific differences in FN expression and its assembly into fibrils exist between these two cell types. Together, our data demonstrate that sdc1 functions to regulate integrin activity in multiple cell types. Loss of sdc1-mediated integrin function results in cell-type specific differences in matrix assembly. A better understanding of how different cell types regulate FN fibril formation via syndecans and integrins will lead to better treatments for scarring and fibrosis.