Random implants

Extraterrestrial dust particles can be proven to be nonterrestrial by a variety of methods, depending on the particle si2e. Unmelted particles have high helium. He, contents resulting from solar wind implantation. In 10-)J.m particles the concentration approaches l/(cm g) at STP and the He He ratio is close to the solar value. Unmelted particles also often contain preserved tracks of solar cosmic rays that are seen in the electron microscope as randomly oriented linear dislocations in crystals. Eor larger particles other cosmic ray irradiation products such as Mn, Al, and Be can be detected. Most IDPs can be confidently distinguished from terrestrial materials by composition. Typical particles have elemental compositions that match solar abundances for most elements. TypicaUy these have chondritic compositions, and in descending order of abundance are composed of O, Mg, Si, Ee, C, S, Al, Ca, Ni, Na, Cr, Mn, and Ti. 

Fig. 3.49. RBS spectra from GaAs implanted with Si (120 keV, 5 x lO cm before and after annealing at 950 °C. The uppermost spectrum is taken in a random direction, the others are in the channeling direction [3.127],...

Isotropic carbon is obtained by the pyrolysis of a hydrocarbon, usually methane, at high temperature (1200-1500°C) in a fluidized bed on a graphite substrate.Under these conditions, a turbostratic structure is obtained which is characterized by very little ordering and an essentially random orientation of small crystallites. In contrast to graphite which is highly anisotropic, such a structure has isotropic properties (see Ch. 7). Isotropic carbon is completely inert biologically. Its properties are compared to alumina, another common implant material, in Table 17.8. Notable is its high strain to failure. 

More definitive evidence of enzymatic attack was obtained with 1 1 copolymers of e-caprolactone and 6-valerolactone crosslinked with varying amounts of a dilactone (98,99). The use of a 1 1 mixture of comonomers suppressed crystallization and, together with the crosslinks, resulted in a low-modulus elastomer. Under in vitro conditions, random hydrolytic chain cleavage, measured by the change in tensile properties, occurred throughout the bulk of the samples at a rate comparable to that experienced by the other polyesters no weight loss was observed. However, when these elastomers were implanted in rabbits, the bulk hydrolytic process was accompanied by very rapid surface erosion. Weight loss was continuous, confined to the... 

One of the more important applications of ion implantation is well engineering at relatively high ion energies. For the protection of dynamic random access memories from soft errors, different structures have been proposed and employed. The conventional procedure is to use epitaxial wafers well engineering beneath the active p- and n-channels provides a less expensive alternative. 

Betriu A, Masotti M, Serra A, et al. Randomized comparison of coronary stent implantation and balloon angioplasty in the treatment of de novo coronary artery lesions (START) a four-year follow-up. J Am Coll Cardiol 1999 34 1498-1506. 

Implantable cardioverter defibrillators, on the other hand, have demonstrated a remarkable effectiveness in prevention of SCD, with an overall 1-year survival rate of 92% in patients with documented life-threatening ventricular tachyarrhythmias [26]. Three randomized, controlled trials have demonstrated the ICD to be superior to antiarrhythmic medications in the secondary prevention of SCD [27-29]. Recent primary prevention studies have also demonstrated improved... 

Following resuscitation from ventricular fibrillation (VF) or pulseless VT, ICD implantation is a proven strategy for the prevention of recurrent SCD. Three prospective, randomized, controlled trials, the Antiarrhythmics Versus Implantable Defibrillators (AVID) study, the Canadian Implantable Defibrillator Study (CIDS), and the Cardiac Arrest Study Hamburg (CASH), support this strategy [27-29]. 

A significant mortality benefit of ICD therapy was shown in the largest of the three studies, the AVID study. In this study, over 1,000 patients with ischemic cardiomyopathy and an EF < 40% who were resuscitated from VF or from symptomatic, sustained VT were randomized to antiarrhythmic medications (>90% amiodarone) or ICD implantation. The trial was stopped early because the ICD showed a significant survival benefit with an 11.3% absolute and 31.5% RR reduction for all-cause mortality over 3 years. Persistent benefit with the ICD was seen even after adjustment for age, beta blocker use, and baseline EF. 

The Multicenter Automatic Defibrillator Implantation Trial (MADIT) randomized 196 patients with ischemic cardiomyopathy, EF < 35%, a documented episode of nonsustained VT (NSVT), and inducible VT on electrophysiology study (EPS) to ICD versus conventional medical therapy [9]. After a mean follow-up of 27 months, the RR reduction for allcause mortality in the ICD arm was 59% [p = 0.009]. 

Because the above trials showed a >50% relative reduction in total mortality with ICD therapy, MADIT II used broader entry criteria for primary prevention of SCD, removing the criteria for NSVT and EPS 1,232 patients with a history of MI > 30 days prior and an EF < 30% were randomized to conventional therapy or ICD implantation [10]. Conventional therapy was comparable in both arms and included a high rate of use of beta blockers, angiotensin-converting enzyme inhibitors, and statins (over two thirds for all medications in both arms). The trial was stopped early at 20 months because the relative reduction in total mortality... 

Kuck KH, Cappato R, Siebels J, et al. Randomized comparison of antiarrhythmic drug therapy with implantable defibrillators in patients resuscitated from cardiac arrest the Cardiac Arrest Study Hamburg (CASH). Circulation. Aug 15 2000 102(7) 748-754. 

Connolly SJ, Gent M, Roberts RS, et al. Canadian implantable defibrillator study (CIDS) a randomized trial of the implantable cardioverter defibrillator against amiodarone. Circulation. Mar 21 2000 101(11) 1297-1302. 

Ezekowitz JA, Armstrong PW, McAlister FA. Implantable cardioverter defibrillators in primary and secondary prevention a systematic review of randomized, controlled trials. Ann Intern Med. Mar 18 2003 138(6) 445-452. 

The CARE-HF study was a European study of medical therapy alone versus medical therapy with the addition of a CRT pacemaker [119]. A total of 813 patients were enrolled and randomized in a 1 1 ratio prior to device implant, again a true intent-to-treat design. Patients were followed longer than in the COMPANION trial, for a mean of 29.4 months. The primary end point was the time to... 

CRT is now recommended for patients with LVEF less than or equal to 35%, sinus rhythm, and NYHA functional class III or ambulatory class IV symptoms despite recommended, optimal medical therapy and who have cardiac dyssynchrony, which is currently defined as a QRS duration greater than 0.12 ms, unless contraindicated. To date, over 4,000 patients have been studied in randomized clinical trials of CRT. A recent evaluation of complications from those studies suggest a risk of implant mortality of 0.4%, failure to implant a functioning LV lead in 10%, lead malfunction or dislodgement in 8.5%, and pacemaker infection in 1.4% [123]. 

Connolly SJ, Dorian P, Roberts RS, Gent M, Bailin S, Fain ES et al. Comparison of beta-blockers, amiodarone plus beta-blockers, or sotalol for prevention of shocks from implantable cardioverter defibrillators the OPTIC Study a randomized trial. JAMA 2006 295 165-71. 

Figure 4.3 Examples of light ion backscattering channeling spectra of SiC crystals that were randomly implanted with a range of parameters such to produce damage levels extended from low values up to the total disorder, (a) 2 MeV He Rutherford backscattering. (From [48], 2000 American Institute of Physics. Reprinted with permission.) (b) 3.550 MeV He backscattering. (From [31], 2002 Elsevier B.V. Reprinted with permission.) (c) 0.94 MeV D Rutherford backscattering and C(d,p) C nuclear reaction. (From [50], 2002 Elsevier B.V. Reprinted with permission.)...

Random and channeled implanted profiles in 6H-SiC are shown in Figure 4.11(a). These profiles correspond to implants performed at RT with 1.5 MeV AF to a low fluence ( 10 cm" ). The flux is not accurately defined because of the experimental constraints, as explained in [74]. In fact, most of the studies concerning channeled implants make use of ion beams in single- spot configurations and have to face the problems related to nonhomogeneous flux distribution within the beam spot. The... 

Figure 4.10 Damage and doping profiles for the same set of random as-implanted 6H-SIC samples, (a) Comparison between RBS-C measured and MC-BCA simulated damage profiles. (From [73]. 1999 Elsevier B.V. Reprinted with permission.) (b) Comparison between SIMS measured and MC-BCA simulated chemical profiles. (From [72]. 2001 Material Science Forum. Reprinted with permission.)...

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