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PREFACE:

Mechanical engineering is an engineering discipline that applies the principles of physics and  materials  science  for  analysis,  design,  manufacturing,  and  maintenance  of  mechanical systems. 

 This  book  covers  leading-edge  research  in  a  cross-section  of  fields  centering  on mechanical  engineering  including  current  research  data  on  the  fracture  mechanics  of  wood and wood-like reinforced polymers; thulium-doped fiber amplifiers; the role of microalloying elements on the microstructure of hot rolled steels; and high-strength titanium base alloys. 

Chapter  1  -  This  chapter  discusses   the  theory  of  fracture  mechanics  based  on  the  flat elliptical  crack;  the  derivation  of  the  mixed  "mode  I  -  II"  -  interaction  equation,  with  the relations between the mode I and mode II stress intensities and energy release rates, based on an orthotropic-isotropic  transformation  of  the  Airy  stress  function;  the  derivation  of  the softening curve with the explanation of the measurements; the derivation of the power law; the energy method of notched beams and of joints loaded perpendicular to the grain; and the necessary rejection of the applied crack growth models and fictitious crack models. 

Chapter  2  -  Magnetic  resonance  imaging  (MRI)  has  developed  into  one  of  the  most versatile techniques in clinical imaging and biomedical research by providing non-invasively high resolution, three-dimensional anatomical and contrast-enhanced images of living tissue. 

The two most common groups of contrast-enhancing agents are gadolinium-based complexes and magnetic nanoparticles. Both types of contrast agents shorten locally the relaxation time of  bulk  water  protons via  rapid  exchange  of  water  molecules  employing  inner-  or  outersphere  magnetic  interactions  to  provide  T 1-,  T 2-,  or  T 2*-based  contrast  enhancement.  

The quest for disease-specific and individualized approaches to imaging requires contrast agents with  a  relatively  high  sensitivity  and  has  propelled  the  development  of  novel  functional  or target-specific  agents.  With  this  aim,  the  shift  properties  of  paramagnetic  complexes  other than gadolinium have been exploited for designing new types of contrast agents with highly specific  reporter  functionalities.  The  particularly  beneficial  chemical  shift  properties  of thulium(III) and their thermal sensitivity, therefore, have stimulated the development of novel thulium(III)-based  contrast  agents  for  MR  imaging.

  An  important  group  of  such  agents  is formed by those that generate contrast based on the transfer of saturated magnetization from the contrast agent or from water molecules interacting with a lanthanide shift reagent to the bulk water (chemical exchange saturation transfer (CEST) agents).

 Magnetization saturation is created using either exchangeable protons of the paramagnetic thulium(III) chelate complex (paraCEST  agents),  or  using  water  molecules  that  interact  with  a  thulium  shift  reagent encapsulated in a liposomal carrier (lipoCEST agents). Various strategies have already been devised to modulate the CEST effect in response to a physiologically meaningful parameter,such  as  pH,  metabolite  concentration,  or  enzyme  activity.

  MR  thermometry  is  another important  target  in  the  development  of  novel  thulium(III)-based  contrast  agents.  Such temperature  mapping  is  based  on  the  strong  temperature  dependence  of  the  hyperfine chemical shifts of thulium(III) complexes, which can be measured  in-vivo with different MR techniques. Upcoming applications of thulium-based contrast agents include disease-specific targeted contrast agents and theranostic agents suitable for image-guided drug delivery. 

Chapter  3  -  Due  to  the  tremendous  increase  in  communication  traffic  in  recent  years, more  and  more  efforts  in  research  have  been  directed  towards  developing  highly  efficient broad-band fiber amplifiers that will fully exploit the low-loss band of silica fibers in order to increase  the  transmission  capacity  of  wavelength-division  multiplexing  (WDM)  networks. 

These broad-band amplifiers must be able to amplify the new short wavelength band (S-band) in  addition  to  the  existing  C-  and  L-bands.  Thulium-doped  fiber  amplifiers  (TDFAs)  are  a promising candidate for the S-band amplification because the amplification bandwidth of the TDFA  is  centered  at  1470  nm,  which  falls  within  the  S-band.  This  chapter  reviews  the structure and amplification mechanism of various TDFAs.  The mathematical model of single pass  and  double  pass  TDFAs  is  also  described  in  detail.  A  development  of  hybrid  S-band optical amplifier using a TDFA and a fiber Raman amplifier is also presented at the end of this  chapter.  The  wide-band  hybrid  amplifier  is  suitable  for  application  in  S-band  optical telecommunication systems. Chapter 4 - Some micro elements are very sensitive to long time creep rupture properties.

 It is well known that harmful impurities such as S, O, Bi, Sb and Pb diffuse to local areas such  as  grain  boundaries,  interface  between  inclusion  and  matrix  and  surface  of  grain boundary  cavity  during  creep  exposure,  and  accelerate  nucleation  and  growth  of  grain boundary  cavity  and  crack,  which  lead  to  premature  and  low  ductility  grain  boundary fracture. On the contrary, beneficial trace and microalloying elements such as B, Zr, Ca, Ti, V, Nb and Ta counteract the injurious elements by the grain boundary, the interface and the surface refinements, which improve properties of local areas, and prevent premature and low ductility  fracture. 

 In  this  paper  actual  effects  of  these  microalloying  and  trace  elements  on long  time  creep  rupture  properties  of  heat  resistant  steels  are  reported.  In  addition  new microalloying methods preventing grain boundary fracture are introduced.

 At National Institute for Materials Science Japan long time creep rupture data including longer than 100,000h have been obtained on several heats of principal heat resistant materials. The  long  time  creep  rupture  life  and  ductility  show  a  considerable  amount  of  scattering among  several  heats  of  a  same  kind  of  steels,  and  it  was  thought  that  the  scattering  might include  new  effects  of  microelements  on  long  time  creep  rupture  properties,  since  the scattering  is  difficult  to  explain  by  using  well-known  effects. 

 Experimental  results  showed that  main  cause  of  the  scattering  is  difference  in  microelements.  It  was  indicated that  very small amount of Mo and N in solid solution causes the scattering for carbon steels, and also trace of Al content in austenitic stainless steels causes long time creep rupture strength drop. Mo and soluble N atoms in the steels diffuse to dislocations, and the segregated pairs of the elements immobilizes dislocations. The Al in 12Cr and austenitic stainless steels precipitates as AlN at grain boundaries and accelerates nucleation and growth of creep cavities.

 It is found that very small amount of B and N in austenitic stainless steels diffuse to creep cavity surface and cover creep cavity surface by segregationof B or precipitation of BN when S  is  removed  almost  completely.  The  segregated  B  and  precipitated  BN  decrease  surface diffusion rate of creep cavity and also creep cavity growth rateremarkably. The B segregates