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Inclusion of legume in grass pastures optimizes protein values of the forage and promotes improved digestibility. Therefore, we hypothesized that finishing steers on a novel combination of legumes and grass pasture would produce carcasses with acceptable traits when compared to carcasses from steers finished in feedlot systems. In this study, we evaluated the effects of finishing steers on three systems including: grazing legume–grass pasture containing oats, ryegrass, white and red clover (PAST), grazing PAST plus supplementation with whole corn grain (14 g/kg BW (SUPP)), and on a feedlot-confined system with concentrate only (28 g/kg BW, consisting of 850 g/kg of whole corn grain and 150 g/kg of protein–mineral–vitamin supplement (GRAIN)) on growth performance of steers, carcass traits and digestive disorders. Eighteen steers were randomly assigned to one of three dietary treatments and finished for 91 days. Data regarding pasture and growth performance were collected during three different periods (0 to 28, 29 to 56 and 57 to 91 days). Subsequently, steers were harvested to evaluate carcass traits, presence of rumenitis, abomasitis and liver abscesses. The legume–grass pasture provided more than 19% dry matter of protein. In addition, pasture of paddocks where steers were assigned to SUPP and PAST treatments showed similar nutritional quality. When compared to PAST, finishing on SUPP increased total weight gain per hectare, stocking rate, daily and total weight gains. The increase of weight gain was high to GRAIN than SUPP and PAST. Steers finished on GRAIN had high hot carcass weight, fat thickness and marbling score when compared to PAST. However, these attributes did not differ between GRAIN and SUPP. Abomasum lesions were more prevalent in steers finished on GRAIN when compared to PAST. Results of this research showed that it is possible to produce carcasses with desirable market weight and fat thickness by finishing steers on legume–grass pasture containing oats, ryegrass, white and red clover. Moreover, supplementing steers with corn when grazing on legume–grass pasture produced similar carcass traits when compared to beef fed corn only.

The objective of this study was to evaluate the effects of three finishing systems based on concentrate and legume-grass pasture on beef. Steers were finished for 91 days with an exclusively whole corn grain-based (GRAIN) diet, grazed on legume-grass pasture plus 1.4% of body weight of whole corn grain supplementation (SUPP), or grazed on legume-grass pasture (PAST) only. Lipid and myoglobin oxidation, pH, objective color, and α-tocopherol concentrations were evaluated on M. longissimus thoracis steaks. Dietary treatments did not affect pH and minimally affected protein carbonylation. Steaks from steers fed GRAIN were less red, showed higher lipid oxidation during retail display, and higher metmyoglobin formation from day 7 to 13 when compared to PAST. Levels of α-tocopherol were higher in steaks from steers fed diets containing legume and grass. Inclusion of roughage in finishing diets is essential to maintain retail color and prevent lipid and myoglobin oxidation.

Fumonisin B1 (FB1) is a Fusarium spp. mycotoxin which constitutes a major public health issue because of its worldwide distribution and diversity of toxic effects.While the liver and kidney are considered the major target organs of FB1 toxicity in several species, evidence indicates that FB1 may be toxic to the brain. To further investigate the effects of FB1 on the central nervous system the present study aimed to test the hypothesis that acute FB1 exposure causes brain hyperexcitability and the potential underlying mechanisms. For these purposes, adult male C57BL/6 mice were injected with FB1 (8 mg/kg, i.p.) or its vehicle and 30 min thereafter received with a low dose of the classical convulsant pentylenetetrazol (PTZ, 30 mg/kg, i.p.) or its vehicle. After behavioral evaluation the cerebral cortex and the hippocampus were collected for analysis of Na(+),K(+)-ATPase activity, mitochondrial membrane potential (ΔΨm) and mitochondrial complex I and II activities. We found that FB1 reduced the latency for PTZ-induced myoclonic jerks and increased the number of these events. After exposure to FB1 total and α1 Na(+),K(+)-ATPase activities increased in cerebral cortex, whereas the same enzyme activities decreased in the hippocampus. Although no changes in mitochondrial complex I and II activities were found, acute exposure to FB1 increased ΔΨm in the cerebral cortex. Altogether, present results indicate that FB1 causes brain hyperexcitability in vivo, and that mitochondrial dysfunction may represent a potential underlying mechanism.

Pasture-finished beef is becoming more popular among consumers due to concerns related to fatty acid content and sustainable practices. The effects of finishing crossbred steers on legume-grass pasture comprised of oats, ryegrass, and clover (PAST), legume-grass pasture plus whole corn grain (WCG) supplementation (SUPP), and only with WCG (GRAIN) on fatty acids profile, volatile compounds, sensory, and texture attributes were studied. Pasture diets (PAST and SUPP) led to lower n-6/n-3 ratio (P 0.001), and highest deposition of C18:2 cis-9 trans-11 (P 0.001) in the lean. Beef from steers fed GRAIN had the highest values of volatile compounds associated with lipid oxidation. Off-flavor intensity was significantly greater on beef from steers fed GRAIN when compared to PAST. Overall, muscles from steers finished on PAST and SUPP showed similar attributes but differ when compared to GRAIN. The presence of forage is essential to improve fatty acid profile, decrease volatile compounds associated with lipid oxidation, and minimize off-flavor.

Brewer's spent grain (BSG) as a partial substitute for corn silage (CS) was evaluated in finishing feedlot steers on the lipid, protein, color, and microbiological stability of vacuum-packed meat for 75 days under refrigerated storage. Twenty steers were distributed in four treatments in a completely randomized design with five replicates each: 50% concentrate + 50% CS; + 35% CS + 15% BSG; + 25% CS + 25% BSG; and 15% CS + 35% BSG for 90 days. After the animals were slaughtered and the carcasses cooled, the Longissimus thoracis muscle was collected for analyzes. The lipid and protein oxidation, color parameters and microbiological stability of the beef although not affected by the diets (P > .05) oscillated throughout the storage time (P

Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium spp. It has been reported to be a potential cause of liver cancer in rats and esophageal cancer in humans. The underlying mechanisms of FB1 toxicity are thought to be related to the inhibition of ceramide synthase, causing an accumulation of sphingosine (SO) and sphinganine (SA), which in turn may cause tissue functional impairment and the development of oxidative stress. Therefore, in this study, we investigate the effects of an FB1-contaminated diet on markers of oxidative stress in chick liver. A total of 24 male broiler chicks (Cobb 500) were fed a standard control diet or a diet contaminated with FB1 (100mg/kg) for 21 days, starting on postnatal day one. The feed and animals were weighed on days 0, 7, 14 and 21 to estimate the feed conversion ratio, and at 21 days, the liver weight and liver relative weight were determined. At the end of the experiment, samples of blood and liver were collected. The blood was used to quantify the SA/SO ratio, and the liver was used to determine the activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST); ascorbic acid levels (VitC), non-protein thiol (NPSH) levels and TBARS content were also determined. The FB1 diet increased the liver weight, liver relative weight, feed conversion and SA/SO ratio. Furthermore, hepatic TBARS levels, Vit C content and CAT activity were also increased. Conversely, the activities of SOD, GST and NPSH levels, in the liver were not altered by the mycotoxin-contaminated diet. In summary, we showed that subacute exposure of broiler chicks to FB1 induced liver oxidative stress concomitantly with SA/SO accumulation.

Haemangiomas are tumours of vascular origin accounting for approximately 7 % of all benign tumours. Three types of haemangioma have been described according to the vessel type involved: capillary, cavernous and mixed. Intramuscular haemangiomas (IMHs) are infrequent, accounting for less than 1 % of all haemangiomas and are mostly located in the extremities and the trunk. Intramuscular haemangiomas of the rectus abdominis muscle are extremely rare, with only one previous case reported in the literature to the best of our knowledge. In this report, we present the case of a patient with intractable pain related to IMHs of the rectus abdominis and we analyse diagnostic assessment and surgical management of the condition.

L’utilizzo di protesi in chirurgia e oramai ampiamente diffuso, tuttavia permangono ancora alcuni dubbi sulla ipotetica carcinogenicita di tali protesi.

Aquaculture is a very ancient activity: carp breeding appears to date back to 2500 BC. Mollusc culture is an important production activity carried out in marine or lake zones with suitable microbiological, chemical and physical water characteristics and abundant plankton, in which mussels have a prominent role. The study was directed at evaluating the morphometric and quality characteristics of commercial Mytilus galloprovincialis from two culture areas in the mid Adriatic: Ancona (natural and artificial open water cultured area) and Bellaria (only artificial cultured area). Seven samples per area, each weighing 3kg, were collected from June to December. Specimens were examined for size (length, width, thickness, maximum longitudinal and transverse circumference) and weight (total, flesh, shell). The flesh was analyzed to determine its content in moisture, protein, fat, ash, fatty acids and crude energy. ANOVA and χ2 test were applied. Specimens were divided into three length categories (

The electronic exchange in laser-assisted electron-atom scattering is considered. Two processes are studied: i) the elastic 1s-1s transition in hydrogen, that, although not yet available experimentally, allows to get explicit results and insight into the problem; ii) the excitation 11S-23S of helium, of particular experimental interest. For perpendicular geometry, the forward multiphoton cross-sections in hydrogen are dominated by the exchange; the exchange is instead reduced when the classical electron speed in a plane wave is much larger than the incident speed. This last feature is also found with the helium target both for parallel and perpendicular geometry, and leads to interesting predictions when applied to experimental situations recently achieved.

A recently developed method for dealing with the second Born approximation to the laser-assisted potential scattering is applied to the case of superelastic scattering (where no photons are exchanged). The explicit expression of the transition amplitude is analysed in the case of long-range scattering potentials in order to obtain information about the importance of second-order corrections. The analytic properties of the T-matrix in the complex-momentum plane are also studied. It is shown that the field considerably weakens the steep enhancement occurring in the field-free phase of the transition amplitude for long ranges although it does not remove the Coulomb divergence: the field also introduces a new logarithmic singularity, and yields a real part to the existing one, implying an imaginary part to the complex energy. The overall results show the limitations of widely used approximations, and provide evidence of inherent interplay between the radiation field and the static potential.

The theoretical treatment of the one-step multiphoton ionization of atoms in strong fields is extended to include the effects of the field fluctuations. In particular, the case of a field with chaotic fluctuations (namely, with Gaussian distributions of both the field amplitude and phase) is worked out in detail and application is presented to the ionization of hydrogen. The results suggest that the inclusion of the field statistical properties remarkably modifies the findings obtained for the case of a coherent field, the modifications going, as a rule, in the direction of a better agreement with the experimental results. Thus, improvements in the description of the statistical properties of a strong radiation field should be considered as important as the accurate account of the atomic structure and of the dynamics of the ionization process.

The increased availability of sunflower cake, a by-product of oilseed extraction for biodisel production, prompted us to test the scope for its utilization in the diet of Quarter Horses employed in equestrian shows. We substituted 600 and 1200 g of feed with 300 and 600 g of sunflower cake, respectively, so as to obtain isoproteic and isoenergetic diets. Digestibility evaluation by the AIA method evidenced generally improved nutrient utilization with the lower cake diet (300 g sunflower). The higher cake diet was associated with a reduction in the protein digestibility coefficient that was confirmed by higher plasma urea levels.

L’allevamento della capra da latte ha trovato un nuovo impulso in seguito all’aumentata domanda non solo della carne ma anche del latte utilizzato per la produzione di formaggi e per l’alimentazione umana grazie alle sue particolari caratteristiche nutritive. La ricerca ha voluto valutare gli effetti dell’impiego di soia integrale estrusa per sopperire ai fabbisogni energetici e proteici di animali ad alta produzione quali la capra Saanen. La valutazione del profilo metabolico, della curva di lattazione e della qualità del latte permette di dare un giudizio positivo all’impiego di questo alimento.

It is widely acknowledged that day surgical procedures must be performed by expert personnel or carried out under their supervision. Recent regulations introduced by Schools of Postgraduate Surgery oblige postgraduate surgeons to carry out a number of minor and medium-sized operations. The characteristics of day surgery make it an appropriate organisational model for complying with the requirements of these directives. Interventional research has shown that adequate training permits education to be coupled with good results.The postgraduate surgeons are trained to perform hernioplasty using Trabucco's method through surgical training based on an initial phase of at least 20 operated patients during which they act as the second surgeon, and a phase of 10 patients during which they are the first surgeon working alongside a tutor with proven experience. Five doctors are completing their training, having acted as first surgeon assisted by a tutor during the period 01/11/1999 - 31/10/00 in 60 hernioplasty operations using Trabucco's method out of a total of 143 carried out in the same period, with an average of 12 operations each. Specific informed consent was obtained from all patients. All operations were performed under local anesthesia.There was no need to convert to general anesthesia. Complications were comparable to those occurring during surgery performed by experienced colleagues. No recurrences were reported. The mean follow-up was 10 months.An evaluation of these data confirms the real possibility of dedicating a number of ambulatory surgical procedures to training postgraduate surgeons. This would not lead to a reduced efficacy of treatment and does not increase the percentage of complications.

A great variety of surgical techniques have been proposed to repair large abdominal incisional hernias, but the best results are achieved using synthetic grafts as in the Rives' or Ramirez' procedure.During the period September 1993-May 2001, a total of 145 patients, 54 males and 91 females, mean age 52 (range 16-88) with large incisional hernia were observed. Ninety-two hernias were bigger than 10 cm. The average follow-up was 3 years (1-72 months). All successfully underwent surgery using the following techniques: 19 (13.1%) simple fascial sutures, 68 (46.9%) implants of retromuscolar polypropylene grafts (Rives' or Ramirez' technique), 24 (16.5%) subcutaneous meshes, 17 (11.7%) preperitoneal meshes (14 polypropylene, 2 glycolic acid, 1 Goretex), 4 (2.75%) intraperitoneal implants of polypropylene meshes, 13 (9.05%) intraperitoneal glycolic acid grafts plus retromuscular polypropylene graft.One patient died in postoperative for heart failure. Morbidity was 8 subcutaneous hemorrhagic suffusions, 10 seromas which were resolved by repeated percutaneous drainage, 4 suppurating wounds that did not require graft removal, 2 little recurrences treated by a new mesh repair under local anaesthesia, 2 sinus for mesh intollerance and 1 fistula requiring a new intervention.In this report we discuss the tolerability and reliability of mesh repair, especially in Rives' and Ramirez' technique.

Myelolipoma is a rare benign pathology whose pathogenesis is still unclear. It is most frequently localised in the adrenal gland, followed by the presacral region, mediastinum, and perirenal and hepatic region. It varies in size from a few millimetres to several centimetres. The lesion is usually capsulated, detachable from the surrounding tissues and hypovascularised. In histological terms, it is composed of lipomatous and hematopoietic tissues. A 65-year-old female patient was referred to our unit after the finding of a nonbiopsied, pelvic mass during earlier surgery. The patient was in considerable pain owing to the extrinsic compression of the mass on abdominal and pelvic organs. Preoperative tests confirmed the presence of a voluminous presacral neoformation that appeared to have a possible medullary origin (chordoma or schwannoma). During surgery, the lesion was found to be capsulated and mainly adherent to the rectum. Histological analysis confirmed the myelolipomatous nature of the lesion. A review of 21 cases reported in the literature is presented.

A formal method is presented to evaluate the second-order Born approximation of the laser-assisted potential scattering. It is an implicit closure technique that includes intermediate virtual-state transitions and enables one to find the exact explicit expression of the transition amplitude. This is of interest from two standpoints: first, one can deal with ranges of parameters in which the first-order Born approximation is a poor one; second, one can set limits of on-shell approximations that are also widely used to analyze recent laser-assisted experiments. The off-shell character yields new terms in the exact amplitude, and in particular, it is shown to play a crucial role in forward scattering from a long-range potential.

The paper examines the role of ranitidine in the prevention of postoperative hyperamylasemia, a complication following major biliary tract surgery, especially if associated with intraoperative cholangiography. Forty patients underwent cholecystectomy and intraoperative cholangiography: calculosis of the choledochus was observed in 11 patients and a revision of the VBP was therefore carried out involving the transcystic insertion of Kehr's tube. Patients were randomly subdivided into two groups: group A (treated with 50 mg ranitidine 4 times a day e.v.) and group B (no anti H2 treatment). No significant differences were noted between the two groups with regard to the onset of hyperamylasemia, although it is worth reporting that ranitidine virtually eliminated all hemorrhagic complications due to ulcer or postoperative gastritis.

The authors focus on the application of adaptive end-to-end windowing as a reactive congestion control mechanism for data communications over asynchronous transfer mode (ATM) networks. In particular, an adaptive window mechanism including go-back (n) retransmission is proposed. The performance achievable by its application was evaluated by simulation under a particular network model assumption. The gain possible in terms of improvement of cell acceptance is estimated with different source traffic descriptors and network parameter values. Some comments on the interaction between the window mechanism and other congestion control mechanisms for ATM networks are given. >

Multiphoton free-free transitions within a full second-order treatment of the scattering potential are considered with two specific aims: (i) to test some widely used approximations against exact calculations; (ii) to present differential cross sections for the laser-assisted positron scattering, in the regime of intermediate field intensities (up to ${10}^{13}$ W/${\mathrm{cm}}^{2}$). In the case of a field linearly polarized along the incident particle momentum, the results clearly discriminate among the approximations, setting interesting limitations to each of them as functions of the scattering potential features and of the field parameters. Each approach shows good performance for particular scattering angle ranges, pointing to the need for improved techniques to work out fully reliable and easy-to-handle approximations.

This paper deals with the role of the final state interactions in the multiphoton ionization of atoms by strong radiation fields. Considerable work has been devoted to this topic, and several aspects of it have been evidenced to various degrees along the years. The early papers neglected at all the interaction between the ejected electron and the residual ion1, and no systematic calculation was performed at orders higher than the lowest one; nevertheless, these early approaches qualitatively predicted most of the above-threshold-ionization phenomenology and only now it is becoming clear their actual potential and limits2, 3. Other approaches have tried to deal with the final state interactions suggesting that the experimental findings could be explained by means of electron scattering by the parent ion after the ionization4 or by ponderomotive scattering of the ejected electrons when leaving the laser beam5. This latter approach describes the ejected electron by a Volkov wave and let the electrons experience the time and space inhomogeneities of the laser beam, causing significant modifications of their energy and angular distributions. The experimental results appear qualitatively well reproduced by treatments relying on these mechanisms, which thus should be seriously considered for inclusion in a comprehensive, rigorous theory.

The strong-field multiphoton ionization of atoms is considered and a theoretical approach dealing nonperturbatively with the radiation field formulated. The general computational scheme is the conventional perturbation theory, but the intermediate states are dressed by the field. We present in detail a method to dress the continuum states and to study the dipole transitions within the continuum. In the high-frequency domain, the proposed procedure rapidly converges over a wide range of field intensity and offers an interesting framework for calculating ionization rates for arbitrary numbers of absorbed (above-threshold) photons and field polarization.

The problem of charged-particle scattering in the presence of strong laser fields is investigated within a treatment in which the effect of the assisting field is included exactly, to all orders. Two laser field models are considered: 1) the model of a purely coherent field and 2) that of a field with well-stabilized amplitude and fluctuating phase (phase diffusion model, PDM). The scattering cross-sections are numerically investigated for selected but representative values of the parameters of the problem. Differential and total cross-sections are evaluated as functions of the scattering angles, the incident energy, the field coherence and intensity and the number of exchanged photons. The band width of the PDM field is found to affect significantly the scattering parameters, especially in the case of differential cross-sections and of high intensities. As compared to the purely monochromatic (SM) field, the PDM field is found to exhibit oscillations of smaller amplitudes with a tendency to a smooth behaviour with increasing band width, photon multiplicity and intensity. The PDM cross-sections are generally slightly larger than the SM ones. For the first time are reported calculations of the total cross-sectionsvs. the intensity with a sufficiently large density of points to resolve accurately the oscillatory structure of the high-intensity portion of the cross-sections. A consequence ensuing from the exact treatment of the laser field is that the field coherence properties too are treated exactly, at least within the given laser models, and it is expected to be of importance beyond the particular problem treated here, especially when nonresonant processes are concerned.

The multiphoton ionization of helium by a strong radiation field having a wavelength of 1064 nm and a field intensity up to 5 × 1014 W cm −2 is considered within a non-perturbative treatment partially accounting for the electron-electron correlations in the initial bound state and approximately for the Coulomb interaction between the residual ion and the ejected electron in the final state. Only single-electron transitions are considered, the main emphasis being on the field polarization effects. The obtained results are compared with the few results available in the literature in the same regime as well as with very recent experimental findings. In particular, the calculated photoelectron energy spectra, angular distributions and ionization rates are found to reproduce satisfactorily all the main features observed in the experiments. The proposed formalism appears to be a particularly flexible method for studying field polarization effects; for the channel-by-channel analysis in the case of stro...

Within a non-perturbative treatment of the multiphoton multichannel ionisation of helium the authors show for the first time that the angular distributions of the electrons ejected by elliptically polarised light exhibit the twofold symmetry recently observed experimentally on noble gases and already predicted by the authors for hydrogen. Several fine structures and details of the experimental angular distributions are successfully reproduced; a physical model for such asymmetries is provided, which is also able to explain why several approximations fail in reproducing them.

The modifications induced by a magnetic field of arbitrary direction and intermediate strength (i.e not larger than 2.35·105 tesla, the «atomic tesla») on the lowest singlet and triplet energy states of the hydrogen molecule are studied. Using a linear combination of products of field-modified atomic orbitals, it is found that increasing the field strength the depth of the singlet energy well increases and the equilibrium internuclear distance decreases, yielding more rigid and localized nuclear vibrations. For sufficiently strong fields perpendicular to the internuclear axis, the triplet state exhibits a bonding behaviour. An explanation of the above results is given in terms of the field-modified electronic-charge distributions in the internuclear region.

The authors extend to arbitrary polarisation a theoretical treatment of multiphoton multichannel ionisation of hydrogen by a strong laser field that is based on the S-matrix formalism and takes into account the Coulomb interaction in the final state. The effect of laser polarisation in modifying the distribution of electrons in accessible multiphoton channels is analysed. Comparison is made of the numerical results obtained for two models of a laser field, purely coherent and chaotic, showing the importance of considering the radiation properties in this kind of processes. Calculated photoelectron spectra (particularly for the chaotic case) show a good qualitative agreement with known experimental results for rare-gas atoms.

A theoretical model is presented to treat the elementary act of strong-field multiphoton ionization of atoms when the electron continuum final-state distribution is important. It is based on theS-matrix formalism and treats the final-state electron-radiation interaction in an essentially nonperturbative way. Selected numerical calculations concern the ionization of hydrogen atoms and include differential and total cross-sections of several multiphoton channels as a function of the laser intensity. Good, qualitative agreement with the experimental observations is found for values of the field intensity which are not critical with respect to the simplifications adopted in constructing the theoretical model. It applies particularly to the use of an ideal model for the laser field. Significant departure from observations is instead found when the implications of the ideal laser model play a critical role, as occurs at channel inversion and suppression. It is concluded that the theoretical treatment to be completely satisfactory needs essentially to incorporate a more realistic laser model such as a multimode one.

Within a non-markovian treatment of the phase fluctuations of a radiation field (phase diffusion model) and a non-perturbative theory of laser-assisted electron scattering, we show that in very intense fields tha lifetime of the particle energy states may be reduced to such an extent to make invalid the markovian approximation for the field. It is due to the many real and virtual multiphoton exchanges, occuring during the collision event. Thus, the range of applicability of the markovian approximation appears to be restricted to the domain of weak particle—field coupling.

The authors report numerical calculations showing that the well known sum rule for multiphoton-free-free transitions does not hold, contrary to expectations, at small scattering angles. Compared with the field-free results, significant enhancement occurs in both the differential and total cross sections when scattering at small angles is important, especially in the case of strong particle-field coupling and relatively high incident energy (a few hundred eV). A derivation is also reported showing explicitly the new restrictions to the range of validity of the sum rule.

We reconsider the problem of a two-level system interacting with a radiation field in order to study some new features suggested by the actual experimental conditions. Pulse shape and duration effects are included in the formalism and the counter-rotating terms are retained. The criterion of validity of the rotating wave approximation (RWA) for pulsed fields is investigated; generalizing results well known in RWA, we establish some new formal results, including non-RWA contributions to all orders and for any pulse shape. The analysis is then carried out for fluctuating fields, by developing a method based on the theory of multiplicative stochastic differential equations. For short pulses, the non-Markovian character of the stochastic field parameters is expected to affect the process and, for broadband fields, the RWA has to be checked ab initio. Thus, a formalism is proposed which allows the study of both features. A wide range of numerical calculations are presented, clarifying the role of both...

TheS-matrix formulation of multichannel multiphoton ionization of atoms is discussed from the standpoint of gauge consistency. As limiting cases the Keldysh approximation (gauge of the electric field) and a related approximation used by different authors in the radiation gauge are considered in detail. The relation existing between the two approximations is shown. It is also shown that the approximation formulated in the radiation gauge is based on a procedure which is essentially hybrid from the gauge standpoint. In the radiation gauge, a new approximateS-matrix has been derived which is demonstrated by formal considerations and numerical analysis to be the closest counterpart of the Keldysh result. The reported calculations show that gauge consistency is important in approximate treatments of nonresonant multiphoton ionization. The results based on hybrid procedures, when operators and wave functions are not consistently and simultaneously transformed, may depart by orders of magnitude from the results of approximations which are equivalent as to the level of description of the physical process, but essentially correct as to the requirements of gauge consistency.

The role of the initial electronic configuration in the multiphoton ionisation of two-electron atoms is studied by considering three different wavefunctions to describe the ground state of helium. The theoretical treatment of the multiphoton process is an extension to a two-electron problem of the non-perturbative Keldysh model. Though the initial electronic charge distributions predicted by the chosen wavefunctions are largely similar, the ionisation rates provided by them are found to differ by orders of magnitude when the number of photons required to ionise increases. Accordingly, an accurate description of the initial electronic configuration in a process which is highly non-linear is found necessary. Besides, as a process involving a large number of photons may occur only in the presence of a sufficiently strong Coulomb field, it is argued that a multiphoton process may be used as a probe of the electronic correlation in atoms.

The authors present a theory of the potential scattering in the presence of a laser field taken with a well stabilised amplitude and a randomly fluctuating phase (phase diffusion model, PDM), and investigate the structure of the scattering lineshapes in the weak- and strong-field limits. The field, with its statistics, enters the theoretical treatment in a non-perturbative way. This gives the possibility of obtaining new information on the role of the statistical properties of the radiation fields in highly non-linear domains of the matter-field interaction, which complements in a significant way what is presently known. The PDM results are compared with those relative to a chaotic field (multimode laser field with a large number of uncorrelated modes). The broadening of the scattering lines is found to be controlled in an essential way by several parameters (field bandwidth, strength of the particle-field coupling, field intensity and so on); among them, the multiplicity of the exchanged photons becomes the most important only in the limit of weak coupling. In the strong-coupling limit, a chaotic field (i.e. a field undergoing amplitude and phase fluctuations) is found to broaden the scattering lines in a more effective way than a PDM field.