presentation of its subject which, by having collected in one place a comprehensive assortment of methods and techniques of measurement, will be of value to any person interested in comparing the possibilities and limitations of each. It is most certainly recommended to the audience for which it is written. Mechanics of Composite Materials. By Robert M. Jones. McGraw-Hill Book Company, New York. 1975. xiv + 355 Pages. Cost $21.00. REVIEWED BY C. W. BERT* With the rapid development of high-performance fibers and their increasing use in critical structural applications, there is a great need for a text which covers the topics peculiar to the mechanics of such structures: micromechanics, macroscopic anisotropy, and flexural-extensional coupling. Professor Jones has drawn from his extensive industrial and pedagogical experience in the relatively new field of composite material mechanics to write a textbook which serves this need very well. The introductory chapter gives an up-to-date overview of the types, terminology, manufacture, current applications, and future potential of composites. Chapter 2 is devoted to macroscopic stiffness and strength behavior of a single layer. Chapter 3 is concerned with micromechanics, i.e., prediction of the composite stiffness and strength behavior from known properties and geometric configuration of its constituent materials (the fibers or other reinforcements and the matrix). Chapter 4 covers laminate mechanics, i.e., prediction of laminate behavior from known properties, arrangement, and orientation of the individual layers. Problems of stable static deflection, static buckling under in-plane loads, and free vibration of laminated, composite-material plates are presented in Chapter 5. Chapter 6 treats briefly the following miscellaneous topics: fatigue, fracture mechanics, effects of holes, transverse shear effects, and environmental effects.

We have ionized Rydberg atoms using subpicosecond half-cycle electromagnetic pulses. The threshold electric field required to ionize a Rydberg state with effective quantum number AZ* is found to scale as n*~2 for states with n* > 13 in contradistinction to the n*~4 threshold scaling for static field ionization and high order multiphoton ionization. This novel result is explained using a classical model. PACS numbers: 32.80.RmThe ionization of atoms by pulsed electromagnetic radiation has been studied using pulsed lasers [1], microwaves [2,3], and ramped dc electric fields [4]. However, until very recently, the temporal width of available pulses was quite large compared to the internal time scales of the atoms under study. In the last decade, however, ultrashort (< 100 fs) laser pulses have been produced, which have durations of only tens of optical cycles [5,6]. Ionization in these laser fields can differ drastically from ionization with longer pulses because the large laser bandwidth may coherently excite several atomic states [71.We have extended the study of ionization by coherent broadband laser pulses to its logical limit by employing ultrashort, half-cycle electromagnetic pulses. Half "optical-cycle" pulses with widths T < 200 fs have been created in photoconducting semiconductor switches illuminated by 100 fs laser pulses [8]. These freely propagating electromagnetic pulses have central frequencies around 1 THz (33 cm -1 ). We have succeeded in increasing the available pulse energy by more than an order of magnitude, and have demonstrated that peak fields in excess of 100 kV/cm can be produced in a nearly unipolar 500 fs electric field pulse [9]. While these fields are still insufficient to ionize the ground state of atoms, they are quite capable of ionizing high-lying Rydberg states.We have studied the ionization of Na Rydberg atoms using freely propagating, 500 fs single-polarity pulses. Complete ionization of Rydberg states with principle quantum number n > 13 is observed. We show that Rydberg states subjected to these short pulses begin to ionize when the peak electric field is proportional to their binding energies. In contrast, ionization of atoms by relatively long (JAS) microwave pulses and ramped dc electric fields requires peak fields which scale as n ~5 and n ~4, respectively [3,4]. The novel threshold field scaling can be explained by classical mechanics.In the experiment, two tunable dye lasers excite ground state Na atoms to a Rydberg state. The half-cycle pulse (HCP) is then weakly focused on the Rydberg atoms. Any ions formed by the HCP are collected using a microchannel plate (MCP) detector. We record the number of ions (or electrons) which are produced as a function of the peak electric field in the HCP.The source of the HCP [10] is a thin (0.5 mm) GaAs semiconductor wafer with a surface area of -3 cm 2 . An electric field (F<10 kV/cm) is applied parallel to the surface of the GaAs. The electric field is then shorted across the semiconductor surface by illuminating one side of the wafer w...

We have generated sub-single-cycle pulses of electromagnetic radiation with pulse energies as high as 0.8 ,tJ and pulse lengths < 500 fs. The 10-dB width of the spectrum is 1.5 THz. The transmitter is a GaAs wafer illuminated at normal incidence by 120-fs, 770-nm pulses from a Ti:sapphire chirped-pulse amplifier system while a pulsed electric field is applied across the surface. The pulse energy of the far-infrared radiation is found to be a quadratic function of bias field and a nonmonotonic function of laser intensity.

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Composite tubes can be reinforced with continuous fibers. When such tubes are subjected to crushing loads, the response is complex and depends on interaction between the different mechanisms that control the crushing process. The modes of crush ing and their controlling mechanisms are described. Also, the resulting crushing process and its efficiency are addressed.