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The detailed physics of the light–matter interaction will of course also depend on the structure of the irradiated molecule, but whatever its identity, certain general features of the excitation of atoms and molecules by ultrafast laser photons have emerged from pioneering studies by research groups through- out the world. First to respond to the laser ﬁeld are the lighter electrons, which do so on a time scale of attoseconds (a thousandth of a femtosecond): depending upon the intensity of the incident light, the one or more photons absorbed by the molecule either promote an electron to a high-lying energy state of the molecule, or the electron is removed from the molecule altogether, leaving a positively charged ion; at very high intensities multiple electron excitation and ionisation through various mechanisms can occur. Over a far longer time scale of tens or hundreds of femtoseconds, the positions of the atomic nuclei within the molecule rearrange to accommodate the new electrostatic interactions suddenly generated as a result of the new elec- tronic state occupancy prepared by the ultrafast laser pulse: the nuclear motions may involve vibrations and rotations of the molecule, or the mole- cule may fall apart if the nacent forces acting on the atoms are too great to maintain the initial structural conﬁguration. In addition, at high incident intensities, the electric ﬁeld associated with the laser beam distorts the electrostatic forces that bind the electrons and nuclei in a molecule to such an extent that the characteristic energy levels of the molecule are modiﬁed during the ultrashort duration of the laser pulse. Each of the above phenomena is the subject of intensive research pro- Laser snapshots of molecular motions 3 grammes in its own right. A similar series of events, with due alteration of the details, occurs in molecules exposed to intense laser light. From careful measurements of such processs, it is possible to develop quantitative models to describe the molecular dynamical response to impulsive laser excitation. These enable the fundamental interaction of intense, ultrafast laser light with molecules to be understood from ﬁrst Laser-distorted atomic electron Ponderomotive potential electron trajectory High harmonic photon emission Tunnel ionisation Figure 1. A sequence of events following the interaction of an intense, ultrafast laser pulse with an atom. The potential energy structure of the electron, which would otherwise be symmetric either side of a minimum, thereby conﬁning the electron to the vicinty of the atomic nucleus, is distorted by the incident laser radiation. The electron ﬁrst escapes (ionises) from the atom by tunnelling through the barrier on the side of lower potential energy and then executes an oscillatory trajectory determined by its kinetic (or ponderomotive) energy in the electric ﬁeld of the laser pulse. If the electron follows a trajectory that brings it back close to the nucleus of the ionised atom, emission of a high-frequency photon can occur as the negatively charged electron is accelerated by the positively charged ion. This high-frequency photon is found to be an exact harmonic (overtone) of the laser frequency originally absorbed by the atom. ROBERTS principles in terms of the wave description of matter and light due to quantum theory. Following a description of femtosecond lasers, the remainder of this chapter concentrates on the nuclear dynamics of molecules exposed to ultrafast laser radiation rather than electronic effects, in order to try to understand how molecules fragment and collide on a femtosecond time scale. Of special interest in molecular physics are the critical, intermedi- ate stages of the overall time evolution, where the rapidly changing forces within ephemeral molecular conﬁgurations govern the ﬂow of energy and matter. Sub- 100fs laser pulses were realised for the ﬁrst time from a colliding-pulse mode-locked dye laser in the early 1980s at AT&T Bell Laboratories by Shank and coworkers: by 1987 these researchers had succeeded in produc- ing record-breaking pulses as short as 6fs by optical pulse compression of the output of mode-locked dye laser. In the decade since 1987 there has only been a slight improvement in the minimum possible pulse width, but there have been truly major developments in the ease of generating and characterising ultrashort laser pulses. The major technical driving force behind this progress was the discov- ery by Sibbett and coworkers in 1990 of a new category of ultrafast laser operation in solid-state materials, the most important of which is sapphire impregnated with titanium (others are the chromium-doped colquiriite minerals). These devices rely upon the intensity dependence of the refrac- tive index of the gain medium to generate powerful, ultrashort laser pulses in a single ‘locked’ mode: a photograph of a commercial titanium:sapphire laser is shown in Figure 1. Titanium:sapphire lasers typically deliver pulses with durations between 4. To overcome this limitation, the peak power of a femtosecond laser can be dra- Figure 1. Photograph of a Tsunami titanium:sapphire laser manufactured by Spectra-Physics Lasers Inc. The lasing transition in Ti:sapphire is between vibrational levels of different electronic states of the Ti3 ion.
In a perceptive study purchase 20mg levitra professional overnight delivery, Margaret May and Edward Brunsdon noted the shift in the 1980s away from traditional ‘occupational health’ concerns towards ‘new “wellness” interventions’ discount 20 mg levitra professional with amex, including medical ‘check-ups’, ‘health risk appraisal’, screening tests and preventive lifestyle advice (May, Brunsdon 1994). They characterised this as ‘a new form of employee control’, far beyond the familiar organisation of work, as the jurisdiction of the employers extended into workers’ private lives. They commented on the convergence of management theory and government health policy around the themes of personal responsibility. The proliferation of workplace smoking bans in the 1990s was another indication of the extension of managerial authority justified by concern for employee’s welfare. As health promotion assumed an ever greater profile, there was some divergence between the ways in which prevention strategies were presented to the public and how they were perceived within the private world of medicine. The politicians and the media wanted simple messages, soundbites, and doctors who took the lead in health promotion campaigns were happy to provide them—on the evils of passive smoking, the dangers of dairy products or the need for screening tests. Meanwhile, as we have seen, a high—and often increasing—level of scepticism came to prevail among medical experts about the value of all these interventions. In fact, in private, many doctors in all specialities are doubtful of the value of much of the work of health promotion. However, recognising the strength of the health promotion consensus, solidly backed by government funding, medical vested interests and compliant journalists, they think it best to keep their reservations to themselves. Indeed, as any of the sceptics who have spoken out could testify, the price of making private reservations about fashionable health promotion interventions public is high. The intellectual insecurity underlying the health promotion consensus is expressed in a dogmatic intolerance of criticism and intense hostility towards any dissident opinion. Anybody who ventures criticism of these policies—or has the temerity to publish research revealing their ineffectiveness—can 66 SCREENING expect a tirade of abuse and little prospect of academic advance- ment. A spirit of ‘not in front of the children’ governs debate as medical science is subordinated to political expediency. The second theme that emerges from our discussion of health promotion interventions is the resulting restriction on individual liberty. This is not so much a matter of direct compulsion, but of the oppressive effect—well expressed by Bridget Jones in her eponymous diary—of living in constant awareness of the need to count cigarettes, calories and units of alcohol (Fielding 1997). When I first received a ‘health risk assessment’ report resulting from the sort of encounter that so incensed Ruth Lea of the Institute of Directors in the account quoted above, I expected that it would provoke a similar response from many patients annoyed by the intrusive and impertinent character of the questions and the patronising style of the advice. The attitude of most people to such procedures appears to have shifted from an earlier bemusement or indifference (combined with some irritation at the amount of time wasted) to a more recent positive enthusiasm for intervention. This outlook extends to patients (invariably, in my experience, fit young men) whose friends have had the full medical, but whose own employers do not stretch to the (considerable) expense. They turn up at the surgery, declaring that they ‘need a complete check-up’. The popularity of the notion that healthy young people require regular medical maintenance marks the triumph of the ideology of health promotion. As Bridget Jones also reflects, guilt is a more common response to health promotion initiatives than anger. When women have come in to the surgery worried about a breast lump, I have occasionally inquired whether they routinely carry out self-examination. The fact that even people who do not follow the dictates of the ‘awareness’ campaigns —in this case into an activity which most experts consider quite useless—still feel that they are in default of their personal and social responsibilities, reveals the impact of health promotion. The gloomy atmosphere of the smokers’ huddle confirms that who defy the injunctions of healthy living experience remorse rather than elation. Over the past twenty years personal behaviour has been exten- sively re-interpreted and reorganised around considerations of health. The very ubiquity of terms which link ‘health’ with some activity which had previously been regarded as a distinct and autonomous sphere indicates this trend—‘healthy lifestyle’, ‘health 67 SCREENING foods’, ‘healthy eating’, ‘sexual health’, ‘exercise for health’. Whereas feminists once rejected ‘women’s health’ as a form of male medical domination, their latter-day sisters have embraced ‘lesbian health’ as an affirmation of identity; in a common spirit of victimhood we now also have ‘men’s health’. The cult of exercise, pursued not for the enjoyment of sporting activity as such, but in the cause of improving physical fitness in the abstract, reflects the ascendancy of preoccupations about health over personal behaviour. The third theme is the transformation of the medical role and the emergence of new institutions that mediate between the individual and the state in the sphere of health. The change in the role of the doctor is most apparent in general practice, in many ways the front line of the advance of medical intervention in lifestyle. In the not-so- distant past, general practice was a demand-led service: patients came to the surgery complaining of illness and doctors offered diagnosis and treatment, care and concern, within the limits of their own abilities and those imposed by medical science and health service resources. Over the past decade, general practice has shifted to a more pro-active approach, inviting patients to attend for health checks and screening procedures and adopting a more interventionist role in relation to lifestyle issues, such as smoking and drinking, diet and exercise.
Con- Paré revues et collationnées sur toutes les édi- troversy and invective order levitra professional 20mg amex, “yellow journalism best levitra professional 20mg,” was tions aver les variantes. Such an exchange, between the his great work on fractures and dislocations, a former associates, Guérin and Malgaigne, led to brief comment on the other is in order. The basic point at issue Ambroise Paré was an attempt to produce, as was an important one. Can the results of clinical Littré had done for the works of Hippocrates, a 218 Who’s Who in Orthopedics deﬁnitive edition. It was a task of great complexity, for Paré had had a long life as a writer (1545–1590) and during this time had not only discussed a tremendous variety of subjects, but had modiﬁed and changed his opinions and doctrines continually. The entire body of Paré’s writing is arranged and ordered with great skill. It is possible to follow the devel- opment of Paré’s ideas on any subject to their ﬁnal form. A considerable portion of the ﬁrst volume is devoted to an introduction, which consists of a history of surgery in western Europe from the sixth to the sixteenth century, ending with a bio- graphy of Paré and a discussion of his work. This introduction is one of the ﬁnest short accounts of the history of surgery extant. It is unfortunate that it was not published separately, as it stands in the John L. MARSHALL shadow of the immensity of Paré’s achievement, and for this reason has not received the attention 1936–1980 that is its due. Marshall died in a light-plane crash on John Shaw Billings, American surgeon and his- February 19, 1980. He had just left the Atlanta, torian, epitomizes the career of Malgaigne: Georgia, meeting of the American Academy of Orthopedic Surgeons and was en route to Lake Malgaigne was the greatest surgical historian and critic Placid, New York, for the Winter Olympics the world has yet seen, a brilliant speaker and writer, as consultant to the US ski team. Although an whose native genius, joined to incessant labour, accomplished pilot, he was a passenger in the brought about a new mode of judging of the merits of plane. He was 43 years old and at the height of a surgical procedures—the mode of statistical compari- remarkably distinguished and productive career. Marshall was Director of Sports Medicine and although he made some improvement in the art, at the Hospital for Special Surgery in New York such as his hooks for the treatment of fractures of the patella, his suggestion of suprathyroid, laryngotomy, City, having founded the Sports Medicine Clinic etc. At the time of his death he had his work of exploding errors, exposing fallacies in rea- become a world-renowned ﬁgure in orthopedics soning, and bringing to bear upon the work of the and sports medicine. His patients included many present day the light of the experience of the past, of famous professional athletes as well as innumer- which his treatise on fractures and dislocations affords able New York City public-school athletes who many excellent examples. At the Hospital for Special Surgery he was an attending surgeon in References the Department of Orthopedics and Director of the Laboratory of Comparative Orthopedics and 1. As such, he lated from the French with Notes and Additions by was intimately involved in undergraduate and John H. Pettier LF (1958) Joseph François Malgaigne and Orthopedic Surgeons and the American College Malgaigne’s Fracture. Stewart FC (1843) The Hospitals and Surgeons of of Surgeons and was a member of numerous Paris. New York, Langley, and Philadelphia,Carey other professional organizations, including the and Hart, p 360 American Orthopedic Society for Sports Medi- cine, the American College of Sports Medicine, 219 Who’s Who in Orthopedics and the Orthopedic Research Society. He was As a teacher, he was exceedingly generous with widely known as team physician for the New his time and private operative cases. As an author, York Giants professional football club and a con- he was particular that homework be done and sultant for the New Jersey Nets basketball team, credit be given to other workers in the ﬁeld. Many the New York City Public School Athletic of his more than 65 scientiﬁc papers appeared in League, and the Cornell University Athletic The Journal of Bone and Joint Surgery. Marshall’s incredible Marshall had his usual several papers on the success seemed to follow from his keen intellect, Academy program, but he also participated in limitless energy, and infectious enthusiasm. He panel discussions as a recognized expert on the was born in Schenectady, New York, on June 16, anterior cruciate ligament. He graduated from Cornell University in were yet to be published, but already his work 1956, excelling academically and athletically in was cited prominently in major textbooks.
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