Chemistry and dust in star-forming regions of space

Stars form from clouds of gas and dust in the interstellar medium. How the tenuous interstellar gas becomes a relatively dense star, and how a new star interacts with its environment, are currently lively and active fields of astronomical research. Since the ubiquitous cosmic dust makes the gas in denser clouds opaque to visual radiation, the main way that we can probe regions of star formation is by detecting radio emissions from molecules that are formed in the gas during the collapse. About 130 different molecular species have been detected in interstellar clouds. Most of these molecular species are formed in a variety of gas phase reactions, but some species depend on surface reactions for their formation. Understanding these chemical routes helps us to describe in detail the physical conditions in the gas during the collapse that leads to star formation and in the interaction of the new star with the cloud in which it was formed. We give three examples of such interactions: We describe how the interaction of a newly-formed hot star interacts with the material close to the star but which was not incorporated in it. We show that the molecules that can be seen in such situations were until recently frozen-out as ices on the surfaces of dust grains. Many young stars have outflows in the form of well-collimated high-velocity jets that impact on nearby interstellar gas to create shocked regions. We show that these shocked regions illuminate and modify the chemistry of those regions. The characteristic chemistry arising enables us to describe the nature of the jet/cloud interaction in detail. Stellar jets widen into general outflows that encounter clumps of denser gas. The outflow from a massive star usually ionised. The interaction between such an outflow and a pre-existing clump creates a characteristic interface chemistry. We describe recent observations that appear to be the first detection of such an interface in a region in which massive stars are forming

Initial Results and Literature Review

Aim: To evaluate the role of stereotactic body radiation therapy in the retreatment of locally recurrent cervical cancers. Brachytherapy is the main choice to treat gynecologic cancers. Methods: Patients with recurrent cervical cancer, previously submitted to radiotherapy, were treated with stereotactic body radiation therapy using a CyberKnife system (Accuray Incorporated, Sunnyvale, California) with a fiducial tracking system. Results: From August 2011 to October 2014, 5 patients have been treated. Median age was 81 years (range, 70-84 years). Two patients were diagnosed with adenocarcinoma endometrioid and 3 with squamous cell carcinoma. Toxicity was scored according to the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria. After a median follow-up of 12 months (range, 8-34 months), no severe (>grade 3) acute/late genitourinary or low gastrointestinal toxicity was observed. Conclusion: Our preliminary results of stereotactic body radiation therapy "simulating" high dose rate for recurrent cervical cancers confirm a minimal toxicity and an optimal outcome. The stereotactic body radiation therapy is an alternative to high dose rate brachytherapy for gynecologic tumors

Optical trapping of nonspherical particles in the T-matrix formalism

The theory of the trapping of nonspherical particles in the focal region of a high-numerical-aperture optical system is formulated in the framework of the transition matrix approach. Both the case of an unaberrated lens and the case of an aberrated one are considered. The theory is applied to single latex spheres of various sizes and, when the results are compared with the available experimental data, a fair agreement is attained. The theory is also applied to binary clusters of spheres of latex with a diameter of 220 nm in various orientations. Although, in this case we have no experimental data to which our results can be compared, we get useful indications for the trapping of nonspherical particles. In particular, we find substantial agreement with recent results on the trapping of prolate spheroids in aberrated gaussian fields [S. H. Simpson and S. Hanna, J. Opt. Soc. Am. A 24, 430 (2007)]

On the rotational stability of nonspherical particles driven by the radiation torque

We calculate the radiation torque exerted by a monochromatic plane wave, either unpolarized or linearly polarized, on aggregates of spheres and investigate the stability of the resulting rotational motion. In fact, neglecting any braking momenta we calculate the component of the electromagnetic torque orthogonal to the principal axis of maximum moment of inertia through the center of mass (transverse torque), as a function of the direction of propagation of the incident field. The aggregates we study are composed of homogeneous spheres, possibly of different materials. The electromagnetic torque is calculated through the transition matrix approach along the lines of the theory reported in our recent paper [F. Borghese, P. Denti, R. Saija and M. A. Iati, Opt. Express 14, 9508 (2006)]. When the transverse component of the electromagnetic torque is small or vanishes the rotational motion driven by the component along the principal axis of inertia may be nearly stable

Optical trapping calculations for metal nanoparticles. Comparison with experimental data for Au and Ag spheres.

We calculate the optical forces on Au and Ag nanospheres through a procedure based on the Maxwell stress tensor. We compare the theoretical and experimental force constants obtained for gold and silver nanospheres finding good agreement for all particles with r < 80 nm. The trapping of the larger particles recently demonstrated in experiments is not foreseen by our purely electromagnetic theory based on fixed dielectric properties. Since the laser power produces a heating that may be large for the largest spheres, we propose a model in which the latter particles are surrounded by a steam bubble. This model foresees the trapping of these particles and the results turn out to be in reasonable agreement with the experimental data

Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar Cells

Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are prepared by electrospinning, and their properties assessed by scanning electron, atomic and lateral force, tunnelling, and confocal microscopy, as well as by attenuated total reflection Fourier transform-infrared spectroscopy, photoluminescence quantum yield and spatially-resolved fluorescence. Highlighted features include ribbon-shape of the realized fibers, and the persistence of a network serving as a template for heterogeneous active layers in solar cell devices. A set of favorable characteristics is evidenced in this way in terms of homogeneous charge transport behavior and formation of effective interfaces for diffusion and dissociation of photogenerated excitons. The interaction of the organic filaments with light, exhibiting specific light-scattering properties of the nanofibrous mat, might also contribute to spreading incident radiation across the active layers, thus potentially enhancing photovoltaic performance. This method might be applied to other electron donor-electron acceptor material systems for the fabrication of solar cell devices enhanced by nanofibrillar morphologies embedding conjugated polymers and fullerene compounds.Comment: 35 pages, 9 figure

Optical Properties of Composite Interstellar Grains: A Morphological Analysis

In the framework of the transition matrix approach, we calculate the relevant optical properties of cosmic dust grains of amorphous carbon and astronomical silicates, modeled as aggregates of spherical monomers. Two mechanisms of aggregation were considered, producing clusters with different structure and degree of fluffiness: ballistic particle-cluster aggregation (BPCA) and ballistic cluster-cluster aggregation (BCCA). Our results are very different from those obtained through computational approaches based on effective medium theories and might have major implications both on the modeling procedure and on the dust-mass balance in the interstellar medium

Ultraviolet Radiation inside Interstellar Grain Aggregates. II. Field Depolarization

We study the polarization of the UV light within the cavities of interstellar grain aggregates modeled as homo- geneous spheres containing several spherical voids. The incident field is a linearly polarized plane wave. We found that field depolarization occurs in all examined cases so that the field within the cavities has the features of an ellip- tically polarized wave. The depolarization of the field does not depend on the material of the grains but on the geometry of the problem only. The implications of this result for the interstellar photochemistry are briefly discussed

Ultraviolet Radiation inside Interstellar Grain Aggregates. I. The Density of Radiation

We study the distribution of energy density inside dust grain aggregates through an approach based on the multipole expansion of the electromagnetic fields. A significant fraction of the energy of the impinging wave is found throughout the interiors of grains. Implications for extraterrestrial prebiotic chemistry are discussed