مثبت ومنفی استفہام اور دعوت غور وفکر
استفہام اثبات کے ذریعے بھی ہوتا ہے اور نفی کے ذریعے بھی سیاق و سباق سے اس کی تعیین ہوتی ہے مثلاً مثبت استفہام کے لیے قرآن مجید میں مندرجہ ذیل آیت دیکھیں:
" أَيَحْسَبُ الْإِنْسَانُ أَلَّنْ نَجْمَعَ عِظَامَهُ" ۔[[1]]
"کیا انسان یہ خیال کرتا ہے کہ ہم اس کی ہڈیاں جمع کریں گے ہی نہیں"۔
قرآن مجید کی مندرجہ ذیل آیات منفی انداز استفہام کی مثال پیش کرتی ہیں :
" أَلَا يَعْلَمُ مَنْ خَلَقَ وَهُوَ اللَّطِيفُ الْخَبِيرُ"۔ [[2]]
The scope of this article is to find out the strengths and weaknesses of M.H. Panhwar’s historical work and to compare it with other scholars of Sindh. He is the initiator of scientific history writing of Sindh and the only historian who tried to uncover the face behind the social organisation of Sindh. According to him, ‘History is the history of production, control over the means of production and production to its final distribution’. The history is more about people than that of the ruling class as people are makers of history. He had vision to analyze things in their correct historical perspective and, in this context, he took support of archeology, as it is the source of scientific truth. Writing history with data acquired through carbon testing is a new phenomenon in Sindh, which was locally introduced by M. H Panhwar.1 M. H. Panhwar, therefore, was one of the pioneers in giving a new meaning to history by including both ruling elites and the common folk, progressive science, crop technology, forest, wildlife, etc.2 He was the first to throw light on areas which were ignored by other historians. According to him, history written before him is full of the accounts of the rulers’ role in relation to their nobles and foes, battles they fought, attacks, palace plotting, mausoleums, folklore, fiction and so on. Accounts regarding contemporary climate, environments, diversion of rivers, courses and the resultant ruination of irrigation systems, migrations, shifting of people, occupations, social life of the populace etc. Found little room in written histories. For instance changes in production and its means, administration and justice, agriculture, land, animal husbandry, irrigation sources and methods of mining, metallurgy, industry and industrial goods, matrimonial institutions, family and children, houses and interiors, art, architecture, archaeology, personal appearance, dresses, ornaments, foods and drinks, taxes, coins and currency, science and technology, foreign contacts, international trades and traders, routes of trades, religious beliefs, philosophy, hygiene, medicine and doctors, superstitions, common citizens, economic conditions, historical geography of bygone ages, classes of work and their relation with one another, household life, customs, entertainments, pastimes, leisure, attitude of man to nature, languages, literature, literary contacts with outside word, learning and thoughts, status of women and children in affluence and extreme poverty.3 Hence, in real sense M.H Panhwar was scholar of Haig’s Raverty’s and Lambrick’s calibre.
Modifications to the surface, structural and mechanical properties of brass have been investigated by using three different kinds of radiation sources. The first radiation source was laser, second one was laser induced plasma ions and the third one was Pelletron accelerator. Brass targets were exposed to various laser pulses ranging from 1200 to 3000 of excimer laser (248 nm, 20 ns, 120mJ and 30 Hz) at constant fluence of 6.4 J/cm2 in oxygen atmosphere (100 Torr). In order to explore the ion induced modification in properties of brass, ions were generated by two different ion sources. The laser induced plasma was employed as a first ion source for the generation of Ni, Si and C ions. Excimer laser (248 nm, 20 ns, 120mJ and 30 Hz) was used for the generation of Ni, Si and C plasma. In order to estimate ion flux and energies, Thomson parabola technique was employed. By using this technique, magnetic field of strength 80 mT was applied on the plasma plume to give appropriate trajectory to generated ions. These ions were detected by solid state nuclear track detector (CR39). In response to stepwise increase in number of laser pulses from 3000 to 12000, the Ni ion flux varies from 60 × 1013 to 84 × 1016 5 ions/cm2 with constant energy of 138 KeV. Similarly Si ion flux varies from 45 × 1012 to 75 × 1015 ions/cm2 with constant energy of 289 KeV. The flux of C ions flux changes from 32 × 1011 to 72 × 1014 ions/cm2 with constant energy of 678 KeV. The second source of ion generation is Pelletron accelerator. Brass targets were bombarded by Ni and C ions of energy 2MeV for various ions flux ranging from 56×1012 to 26×1013 ions/cm2. Scanning Electron Microscope (SEM) and X-Ray Diffractometer (XRD) were used to analyze the surface morphology and crystallographic structure of irradiated brass respectively. Universal Testing Machine (UTM) and Vickers Hardness Tester (VHT) were employed to explore Yield Stress (YS), Ultimate Tensile Strength (UTS) and mirohardness of ion irradiated brass targets. SEM analysis reveals the formation of micro/nano sized cavities, bumps, cones and wave-like ridges with non-uniform shape and density distribution after laser irradiations. Whereas, ion irradiation causes the formation and growth of nano/micro sized cavities, pores, pits, voids and cracks for lower and moderate ion flux (in all cases). At maximum ion flux the granular morphology (in case of brass irradiated by laser induced Ni and Si ions) and dendritic morphology (in the case of brass irradiated by laser induced plasma and Pelletron accelerator C ions) are observed. XRD analysis reveals that no new phases are identified in case of laser irradiated brass. However new phases of CuZnNi (200), CuSi (311) and ZnC (0012) are identified in the brass substrate after laser induced Ni, Si and C ions irradiation respectively. Whereas, no new phases are formed in case of Ni and C ion irradiation obtained by Pelletron accelerator. The variation in peak intensity, crystallite size, dislocation line density and induced stresses along with angular shifting is observed in all cases of laser and ion irradiations. Significant variations in mechanical properties of brass are observed after laser and ion irradiations. The changes in mechanical properties of an irradiated brass are well correlated with surface and crystallographical modifications and are attributed to generation, augmentation, recombination and annihilation of the ion induced defects. The laser and ion induced surface, structural and mechanical modifications of brass are significantly influenced by nature, energy and flux of radiations.