On estimation of the effective height of towers on mountaintops in lightning incidence studies

Towers on mountaintops have more incidence of lightning than towers on the flat ground. Therefore towers on mountaintops are ascribed an effective height that is often considerably larger than the physical height of the tower.In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop and propose a new definition based on an engineering model of lightning attachment. The results can be useful in designing lightning protection of communication/transmission lines and masts on mountaintops.     

Estimation of lightning vulnerability points on wind power plants using the rolling sphere method

The escalating number of wind power plants in many countries makes their reliability and safety of crucial importance. One of the main causes of damages for wind power plants is constituted by lightning. Hence, appropriate tools for the lightning protection of wind power plants are required. We have developed a new computer program in Visual Basic, LPS 2008, which runs over AutoCAD and is able to perform risk assessment on a structure or on a service due to lightning flashes to ground. Computer simulations obtained by using LPS 2008 are presented, and conclusions are duly drawn.     

Dynamics of free-standing films of smecticsC

Summary A system of nonlinear hydrodynamics equations of freestanding films of smecticsC is obtained. The Poisson three-dimensional brackets of the hydrodynamical variables of smecticsC integrated by the width of the film are used. A spectrum of the intrinsic modes is calculated and fluctuation effects are analysed. It is shown that in the main approximation over the anisotropy of the smectic layer only fluctuations of the transverse shifts of the film resulting in the observed effects in light scattering are essential. Work presented at the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30–October 2, 1987.     

Surface tension of free-standing smectic films

A generalized mean-field model, which takes into account the anisotropic interactions between the nearest neighbor molecules (forming free-standing smectic films (FSSFs)) and the stabilizing effect of smectic-air interfaces, has been used for numerically studying the structural and thermodynamic properties of these systems during their layer-by-layer thinning. The results of calculating the surface tension γ of a partially fluorinated liquid-crystal compound formed by 5-n-alkyl-2-(4-n-(perfluoroalkyl-methyleneoxy))pentyl (H10F5MOPP) molecules have demonstrated that the value of γ per FSSF molecule undergoes a stepwise increase during layer-by-layer thinning of the film. The dimensional surface tension during the layer-thinning of a 25 layer FSSF formed by H10F5MOPP molecules varies insignificantly within ∼19 dyn/cm, which agrees with the experimental value (∼14 dyn/cm) for this liquid-crystal compound.     

On the formation of ball lightning

Summary A plasma continuum model for the formation of ball lightning is developed based on a substantial number of reports that the ball is often in the discharge column of a previous lightning stroke. The usual method of setting up the plasma equation for a one-component electron plasma is used. An approximate equation for the plasma is derived from the describing equation which is then solved exactly in terms of the Jacobi elliptic functions. The formation of the ball is based on a nonlinearity of the plasma equation which under certain circumstances permits the field to collapse into a small region. Thiscollapse is interpreted to be ball lightning. The approximate equation derived for the plasma has the same form as a previous equation used to describe the formation of the fireball plasma.

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Riassunto Si sviluppa un modello continuo del plasma per la formazione del fulmine globulare basandosi su un consistente numero di lavori in cui risulta che il globulo si forma spesso nella colonna di scarica di un precedente colpo di fulmine. Si usa il metodo consueto di formulare l'equazione del plasma per il plasma di elettroni ad una componente. Si deriva un'equazione approssimata per il plasma dall'equazione descrittiva che è in seguito risolta esattamente mediante le funzioni ellittiche di Jacobi. La formazione del globulo si basa su una non linearità nell'equazione del plasma che in alcune circostanze permette che il campo collassi in una piccola regione. Questocollasso si interpreta come un fulmine globulare. L'equazione approssimata derivata per il plasma ha la stessa forma di un'equazione precedente, usata per descrivere la formazione del plasma della sfera di fuoco.

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Резюме Развивается плазменная непрерывная модель для образования щаровой молнии, основанная на больщом количестве сообшений, что щаровая молния часто образуется в столбе разряда предыдушей молнии. Используется обычный метод вывода плазменного уравнения для однокопонентной электронной плазмы, Выводутся приближенное уравнение для плазмы, которое затем точно рещается в терминах эллиптических функций Якоби. Образование щара основано на нелинейности в плазменном уравнении, которое при определенных условиях допускает возможность полю коллансировать в небольщую область. Этотколланс интерпретируется как щаровая молния. Приближенное уравнение, выведенное для плазмы, имеет ту же форму, что и предыдушее уравнение, использованное для описания образования файрболов в плазме.

     

Strain analysis of free-standing strained silicon-on-insulator nanomembrane

Based on the ultra-thin strained silicon-on-insulator(s SOI) technology, by creatively using a hydrofluoric acid(HF)vapor corrosion system to dry etch the Si O2 layer, a large area of suspended strained silicon(s Si) nanomembrane with uniform strain distribution is fabricated. The strain state in the implemented nanomembrane is comprehensively analyzed by using an UV-Raman spectrometer with different laser powers. The results show that the inherent strain is preserved while there are artificial Raman shifts induced by the heat effect, which is proportional to the laser power. The suspended s SOI nanomembrane will be an important material for future novel high-performance devices.     

Wet-etch optimization of free-standing terahertz frequency-selective structures

Free-standing frequency-selective surfaces consisting of approximately 10-microm-thick copper films with cross-aperture arrays are found to be tunable toward lower frequencies by means of wet chemical etching. Center frequencies were tuned from 1.57 to 1.53 THz while maintaining high transmittance. Wet etching also adjusts bandwidth, peak transmittance, and sidelobe transmittance. The advantage of the wet-etch technique is demonstrated by employment of these devices as bandpass filters for difluoromethane-based terahertz lasers. Adjustment in aperture dimensions because of etching results in suppression of a competing laser line (133.93 microm) by 15 dB while maintaining high transmittance at the operating wavelength of 192.06 microm.     

Switching properties of free-standing epitaxial ring magnets

We present the results of a study of the magnetic switching properties of arrays of narrow Co(1 0 0) epitaxial ring magnets, with outer diameters between 1 and 2 μm, varying inner diameters and varying film thickness. We discuss measurements and the results of numerical computations of the switching fields for the transition from the vortex state to the ‘onion’ state. A large dependence on the ring width and the film thickness is found.     

The physics of lightning

Despite being one of the most familiar and widely recognized natural phenomena, lightning remains relatively poorly understood. Even the most basic questions of how lightning is initiated inside thunderclouds and how it then propagates for many tens of kilometers have only begun to be addressed. In the past, progress was hampered by the unpredictable and transient nature of lightning and the difficulties in making direct measurements inside thunderstorms, but advances in instrumentation, remote sensing methods, and rocket-triggered lightning experiments are now providing new insights into the physics of lightning. Furthermore, the recent discoveries of intense bursts of X-rays and gamma-rays associated with thunderstorms and lightning illustrate that new and interesting physics is still being discovered in our atmosphere. The study of lightning and related phenomena involves the synthesis of many branches of physics, from atmospheric physics to plasma physics to quantum electrodynamics, and provides a plethora of challenging unsolved problems. In this review, we provide an introduction to the physics of lightning with the goal of providing interested researchers a useful resource for starting work in this fascinating field.     

The physics and fabrication of ultra-thin free-standing wires

Free-standing fine wires of metals, insulators and semiconductors are expected to show both quantum-size phenomena and one-dimensional behaviour in their electrical and thermal properties at low temperatures. We summarise some of these effects and describe the methods for fabricating test structures.     

Dynamics of layer-by-layer thinning of free-standing smectic films

A dynamic model has been proposed for describing the extrusion of a single layer of a liquid-crystal (LC) material into a meniscus from an N-layer circular free-standing smectic film (FSSF). In the framework of this model, the main mechanism responsible for the process of the thinning (extrusion) of the LC material from the N-layer FSSF is based on the appearance of a spatial pressure gradient directed along the radius of the circular FSSF. This gradient is formed due to the difference in the disjoining pressures on both sides of the front separating the N- and (N–1)-layer domains of the smectic film. The proposed model allows taking into account the influence of the meniscus on dynamic characteristics, such as the time required for the complete extrusion of a single layer from the N-layer FSSF and the velocity of propagation of the front separating the N- and (N–1)-layer domains in the process of the thinning of the smectic film formed by molecules of 5-n-alkyl-2-(4-n-(perfluoroalkyl-methyleneoxy))pentyl.     

Optical studies on free-standing polypyrrole films by the photopyroelectric method

Optical spectra of free-standing polypyrrole films were investigated by a novel PhotoPyroElectric (PPE) method. The reflection and absorption spectra in the range 2000–25000 cm^–1 of TsO^–- and ClO ₄ ^su– -doped polypyrrole films were obtained with an experimental setup comprising two pyroelectric sensors. The absorption bands due to electronic transitions to the bonding and antibonding bipolaronic levels appear at 11 000 and 21 500 cm^–1, respectively. Some relevant details in the polypyrrole spectrum in the 2000–5000 cm^–1 range were observed. The absorption band located at 3400 cm^–1 is characteristic for NH stretching vibration. The bands in the 2300–2500 cm^–1 range are ascribed to the vibration of N⁺H groups containing positively charged nitrogen. The PPE spectra also reveal changes of the electronic and vibrational absorption bands after polymer reduction and HCl treatment.     

Studies on characteristics of lightning generated currents in an interconnected lightning protection system

An in-depth knowledge about the characteristics of lightning generated currents will facilitate evaluation of the interception efficacy of lightning protection systems. In addition, it would aid in extraction of valuable statistics (from measured current data) on local lightning parameters. Incidentally, present day knowledge on characteristics of lightning induced current in typical lightning protection systems is rather limited. This is particularly true with closely interconnected protection systems, like the one employed in Indian Satellite Launch Pad-II. This system is taken as a specific example in the present study. Various aspects suggest that theoretical modelling would be the best possible approach for the intended work. From the survey of pertinent literature, it is concluded that electromagnetic modelling of lightning return-stroke with current source at the channel base is best suited for this study. Numerical electromagnetic code was used for the required electromagnetic field solution and Fourier transform techniques were employed for computing time-domain results. A validation for the numerical modelling is provided by laboratory experiments on a reduced scale model of the system. Apart from ascertaining the influence of various parameters, salient characteristics of tower base currents for different kinds of events are deduced. This knowledge can be used in identifying the type of event, as well as its approximate location. A method for estimation of injected stroke current has also been proposed.