90-fs stretched-pulse ytterbium-doped double-clad fiber laser

We report ultrashort, high-energy pulse generation from a side-pumped Yb-doped double-clad fiber laser. The laser is operating in the stretched-pulse regime. It directly generates 4.8-ps, 5-nJ pulses that are extracavity compressed to 90 fs.     

Mathematical model for a noniterative optimization of each system for exploiting solar energy

Summary In order to improve the solar-energy collection, whatever the adopted system may be, it is necessary to make ready a mathematical model which matches the astronomical co-ordinates and the geometric ones on the ground in a sole optimization process. The model here proposed permits such a determination in an analytical way, without utilizing iterative numerical methods, as done till now. The proposed approach to the problem is carried out by using the solid analytic geometry. This means that the required mathematical development is quite brief; it refers to a central-receiver system so as to make it as general as possible, but it is immediately adaptable to any other system of exploiting solar energy.

---

Riassunto Per migliorare la raccolta dell'energia solare, qualunque sia il sistema adottato, è necessario approntare un modello matematico che unisca le coordinate astronomiche e quelle geometriche al suolo in un unico processo di ottimizzazione. Il modello qui proposto permette tale determinazione per via analitica, senza cioè ricorrere a metodi numerici iterativi come fatto finora. L'approccio proposto utilizza la geometria analitica nello spazio, cosí da permettere rapidi sviluppi matematici. Lo studio si riferisce a un sistema a ricevitore centrale in modo da essere il piú generale possibile, ma è immediatamente adattabile ad ogni altro sistema di sfruttamento dell'energia solare.

---

Резюме С целью улучшения сбора солнечной энергии необходимо разработать математическую модель, которая согласовывает астрономические и геометрические координаты на земли в процессе оптимизации. Предложенная в работе модель допускает указанное определение аналитическим путем, без использования итерационных численных методов, используемых до сих пор. Предложенный к проблеме подход использует аналитическую геометрию в пространстве. Исследование относится к центральной принимающей системе, что представляет наиболее обций случай, но может быть непосредственно применено к любой другой системе для использования солнечной энергии.

     

Determination de la densite electronique d'un plasma ionise a partir de la distance entre les pics de la raie ‘permise’ LiI et de la raie ‘interdite’ LiI

The aim of this investigation is to verify the method of measuring electron concentrations in partially ionized plasmas on the basis of a comparison of an ‘allowed’ line [such as the LiI (2s² 2p ²P−2s² 4f ²D) line] and a ‘forbidden’ neighbouring line induced by the ionic field [such as the LiI (2s² 2p ²P−2s² 4f ²F) line]. First, the line profiles are calculated theoretically. They are then compared with the observed profiles. It is found that the separation Δ(N_e) between the intensity maxima of the two lines may be conveniently used for the evaluation of the electron concentration N_e. This method is more convenient than one based on the measurement of the width of the ‘allowed’ line or on measurement of the maximum intensity ratios of the ‘allowed’ and ‘forbidden’ lines.     

Effects of an admixture and fast neutron irradiation on thermal properties of sodium potassium sulphate crystals

The differential thermal analysis curves and the specific heat at constant pressure,C _p, of pure and Cu²⁺-doped sodium potassium sulphate crystals were studied. Different neutron fluences were used up to 2.6×10¹⁰ n/cm², in the temperature range 300–500 K. Impurity incorporation generally increased the specific heat up to a maximum at 5% Cu²⁺ content. The peaks for the doped crystals were shifted to lower temperature as a result of neutron irradiation. This behaviour is discussed on the basis of defects induced by irradiation.

---

Zusammenfassung Es wurden die DTA-Kurven und die spezifische Wärme bei konstantem DruckC _p von reinen, mit Cu²⁺ versetzten Natriumkaliumsulfatkristallen untersucht. Im Temperaturbereich 300–500 K wurden verschiedene Neutronenströme bis zu 2,6×10¹⁰ n/cm² verwendet. Der Einbau von Verunreinigungen erhöht im allgemeinen die spezifische Wärme bis zu einem Maximum bei einem Cu²⁺ Gehalt von 5%. Im Ergebnis der Neutronenbestrahlung verschieben sich die Peaks für die versetzten Kristalle in Richtung niedrigerer Temperaturen. Dieses Verhalten wird auf der Basis strahlungsinduzierter Defekte besprochen.

---

_p . 300–500 2,6 · 10¹⁰ n/². 5%. , . , .

---

---

It is a great pleasure for us to express our deepest gratitude to Prof. Dr. Younis S. Selim for his guidance throughout this work and for providing the irradiation facilities.     

Barkhausen noise and domain structure dynamics in Si-Fe at different points of the magnetization curve

In the present relationship between Barkhausen noise and domain structure evolution along the hysteresis loop in 3% Si–Fe has been investigated. The noise power spectrum has been measured vs. induction during cyclic magnetization of the material at a very low constant rate. The obtained results show that the behavior of the noise power along the magnetization curve can be related to the character of the domain structure rearrangements taking place at different levels of induction. Such a connection is reflected in a relationship between the noise power and the shape of the hysteresis loop. The measured noise power spectra are interpreted through the use of a suitable model. This makes possible to connect the shape of the magnetization curve to the microscopic parameters characterizing the dynamic of the domain wall during a large Barkhausen jump.     

About the Cohomology of the Lie Superalgebra of Vector Fields on ℝ n|n

In this article, we compute the first space of cohomology of Vect (? ^n|n ), the Lie superalgebra of vector fields on the supermanifold ? ^n|n with coefficients in 𝒻 (? ^n|n ), the space of smooth functions on ? ^n|n . We give a super analog of the cohomologies of vector fields that where studied for instance by Fuchs [2 Fuchs , D. B. ( 1986 ). Cohomology of Infinite Dimensional Lie Algebras . New York : Consultants Bureau . [Google Scholar]]. This work allows us to classify the deformations of the action of Vect(? ^n|n ) on 𝒻 (? ^n|n ).     

Exponentiated generalized linear exponential distribution

A new generalization of the linear exponential distribution is recently proposed by Mahmoud and Alam [1], called as the generalized linear exponential distribution. Another generalization of the linear exponential was introduced by Sarhan and Kundu  and , named as the generalized linear failure rate distribution. This paper proposes a more generalization of the linear exponential distribution which generalizes the two. We refer to this new generalization as the exponentiated generalized linear exponential distribution. The new distribution is important since it contains as special sub-models some widely well known distributions in addition to the above two models, such as the exponentiated Weibull distribution among many others. It also provides more flexibility to analyze complex real data sets. We study some statistical properties for the new distribution. We discuss maximum likelihood estimation of the distribution parameters. Three real data sets are analyzed using the new distribution, which show that the exponentiated generalized linear exponential distribution can be used quite effectively in analyzing real lifetime data.     

Stability of the S-essential spectra on a Banach space

In this paper, we give the characterization of S-essential spectra, we define the S-Riesz projection and we investigate the S-Browder resolvent. Finally, we study the S-essential spectra of sum of two bounded linear operators acting on a Banach space.     

Hydrogen bond dynamics and water structure in glucose-water solutions by depolarized Rayleigh scattering and low-frequency Raman spectroscopy

The effect of glucose on the relaxation process of water at picosecond time scales has been investigated by depolarized Rayleigh scattering (DRS) experiments. The process is assigned to the fast hydrogen bonding dynamics of the water network. In DRS spectra this contribution can be safely separated from the slower relaxation process due to the sugar. The detected relaxation time is studied at different glucose concentrations and modeled considering bulk and hydrating water contributions. As a result, it is found that in diluted conditions the hydrogen bond lifetime of proximal water molecules becomes about three times slower than that of the bulk. The effect of the sugar on the hydrogen bond water structure is investigated by analyzing the low-frequency Raman (LFR) spectrum sensitive to intermolecular modes. The addition of glucose strongly reduces the intensity of the band at 170 cm(-1) assigned to a collective stretching mode of water molecules arranged in cooperative tetrahedral domains. These findings indicate that proximal water molecules partially lose the tetrahedral ordering typical of the bulk leading to the formation of high density environments around the sugar. Thus the glucose imposes a new local order among water molecules localized in its hydration shell in which the hydrogen bond breaking dynamics is sensitively retarded. This work provides new experimental evidences that support recent molecular dynamics simulation and thermodynamics results.