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SPECIAL ISSUE PAPER 575

Industrial applications of shock wavesG JagadeeshDepartment of Aerospace Engineering, Indian Institute of Science, Bangalore 560 012, India.email: [email protected]

The manuscript was received on 2 November 2007 and was accepted after revision for publication on 19 December 2007.

DOI: 10.1243/09544100JAERO306

Abstract: Shock waves have been traditionally considered to be an integral part of flow fieldfeatures in the area of high-speed aerodynamics. Physically the propagation of shock waves inany media is invariably associated with instantaneous increase in pressure and temperaturebehind the shockwave. The capability of shock waves to generate non-linear pressure and tem-perature spikes in the medium of propagation finds very interesting applications in variety ofareas such as medicine, biological sciences, material processing, manufacturing, and microelec-tronic industries. This paper reviews four new industrial applications of shock waves that havebeen developed in the Shock Waves Laboratory (SWL), Department of Aerospace Engineering,IISc, Bangalore. They are shock wave assisted (a) cell transformation, (b) preservative injectioninto Bamboos, (c) sandal oil extraction, and (d) removal of micron size dust from silicon wafersurfaces. The shock waves generated in an underwater shock wave generator are exploited insuccessfully injecting the desired deoxyribonucleic acid into Escherichia coli and Agrobacteriumcells. The vertical shock wave reactor is applicable in successfully injecting the water-solublechemical preservative (copperchromearsenic) to samples of bamboo. The exposure of sandal-wood samples to shock wave loading in the horizontal diaphragmless shock tube resulted in thedrastic reduction (40 per cent) of time required for oil extraction. Further, a new shock waveassisted technique for micron-size dust removal from silicon wafer surfaces has been devel-oped in collaboration with the Interdisciplinary Shock Wave Research Center, Tohoku University,Sendai, Japan. The strong vortex field generated behind the Mach reflection of a shock wave hasbeen used to remove micron size dust particles from the surface of silicon wafers. The salientfeatures of these new industrial applications of shock waves are described in this paper alongwith some important results.

Keywords: shock waves, cell transformation, preservative injection, oil extraction, dust removal

1 INTRODUCTION

The presence of shock waves is commonly associatedwith aerospace engineering/astronautics and in par-ticular with supersonic flight. These waves appearin nature whenever the different elements in a fluidapproach one another with a velocity larger thanthe local speed of sound [1]. The shock waves arestrong perturbations in aerodynamics that propagateat supersonic speeds independent of the wave ampli-tude. Such disturbances occur in steady transonic orsupersonic flow, during explosions, lightening strokes,and contact surfaces in laboratory devices. The typicalthickness of the shock front in air is typically 107 m,very small compared to other characteristic lengths in

fluid flow. Physically the occurrence of shock wave isalways characterized in a fluid flow by instantaneouschanges in pressure, velocity, and temperature.

Shock wave can be classified as weak or strongdepending on the value of the pressure jump acrossthe shock; they are also classified as normal or obliqueshocks, compression or rarefaction shocks, and director reflected shocks. Due to instantaneous changes influid velocity and pressure, the shock waves gainedlot of attention and are being tried for effective usagein many medical, biological, and industrial applica-tions [2]. It is possible to generate spherical shockwaves with typical radius of few millimetres, both inambient air as well as in water expending energy ofthe order of few joules. For example, in the laboratory,

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576 G Jagadeesh

spherical shock waves can be generated by focusing anNd:YAG (neodymium-doped yttrium aluminium gar-net) laser beam in ambient air and typically the energyexpended in this process is 1.38 J, which is equiva-lent to a 0.3 mg of conventional tri-nitro toluene (TNT)explosive. Figure 1 shows the evolution and reflectionof spherical micro-shock waves generated by focus-ing an Nd:YAG pulsed laser beam from planar surface.Considering the amount of energy spent in generat-ing such shock waves, they deserve to be referred to asmicro-shock waves [3]. However, these micro-shockwaves travelling at supersonic velocity exhibit highlynon-linear pressure profile with ultra short rise time(approximately few microseconds) and are completelydifferent from conventional acoustic waves whereinthe pressure profiles are more linear with slower risetime (approximately tens of milliseconds). On theother hand, it is possible to generate shock waves ofrequisite strength in any desired medium using vari-ety of techniques such as micro-explosions, pulsedlaser beam focusing, electrical discharge in water, spe-cial purpose diaphragmless shock tubes, actuation ofpiezo-electric array, and even bursting of helium bal-loons. The peak pressure behind a shock wave rangesfrom 0.1 100 MPa and the typical pulse width can beanywhere from fews 50s. Whenever the requiredpeak pressure is more than couple of MPa, the gener-ated spherical or planar shock waves are focused usingeither parabolic or ellipsoidal reflectors.

The non-linear instantaneous pressure spike pro-duced for very short time can be used for variety ofapplications in biological as well as in medical sci-ences. The shock wave assisted lithotripsy is probablyone of the most useful and proven treatments forkidney stones [4, 5] and gall bladder diseases, and is

now widely used by doctors in many countries. Theshock waves for lithotripsy are usually of microsecondduration with peak pressures ranging 35120 MPa in asingle pressure pulse. The other applications includetreatment of pancreatic and salivary stones, and inorthopaedics [6].

While substantial progress has been made in theresearch related to medical applications of shockwaves, to the best of authors knowledge, there hasbeen no reported work on shock wave-based applica-tions in agriculture and biological sciences. The non-linear instantaneous pressure spike produced for veryshort time can be used for variety of industrial appli-cations. In the subsequent sections, four innovativeindustrial applications of shock waves that have beendeveloped in the Shock Wave Laboratory, Departmentof Aerospace Engineering, Indian Institute of Science,Bangalore are described. They are shock wave assisted(a) cell transformation, (b) preservative injection intobamboos, (c) sandal oil extraction, and (d) removal ofmicron size dust from silicon wafer surfaces. Despiteall these applications are diverse and different fromone another, all of them utilize the non-linear pres-sure and thermal spikes generated by the propagationof the shock wave in the fluid media in a useful fashion.

2 INDUSTRIAL ENGINEERING APPLICATIONS OFSHOCKWAVES

2.1 Shock wave assisted Escherichia coli andAgrobacterium tumefaciens transformation

Nowadays many of the mind-boggling developmentsin biological science owe its genesis to the capability

Fig. 1 Visualized evolution and reflection characteristics of micro-shock waves generated in thelaboratory using Nd:YAG pulsed laser beam focusing in atmosphere

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Industrial applications of shock waves 577

of biologists in genetically manipulating living cells.Introduction of different macromolecules like DNA(deoxyribonucleic acid), mRNA (messenger ribo-nucleic acid), proteins, and peptides into living cellsis a part and parcel of genetic transformation proto-cols. Genetic transformation essentially refers to theprocess of introducing the particular DNA of inter-est into cell without damaging/destroying the livingcell. The process of Escherichia coli (E. coli) cell trans-formation is schematically shown in Fig. 2. Since theE coli bacteria is an unicellular organism, it is invari-ably used as template to validate any new genetictransformation method in the laboratory. Recently[7, 8], an underwater electric discharge unit (Fig. 3)has been developed for carrying out non-contact typegenetic transformation. One of the major advantagesof the present method over other existing methods isthe fact that there is virtually no contamination duringthe transformation process.

Spherical micro-shock waves (peak overpressuresup to 100 MPa) are generated in water by instanta-neously depositing electrical energy (100 J) betweentwo stainless steel electrodes (1 mm apart) for

Fig. 2 Schematic diagram depicting the bacterial celltransformation process

Fig. 3 Schematic diagram of the underwater shock wavegenerator used in naked plasmid DNA transfor-mation process

about 0.35s. The high voltage applied between theelectrodes can be varied to generate shock wave of req-uisite strength. A high precision mechanical traversesystem was used to hold microfuge tubes contain-ing bacterial cells with the naked plasmid DNA abovethe electrodes. The distance between bottom of thetube and electrodes is maintained at 1.5 mm andcorresponding pressure measured (PVDF (Polyvinyldifluorine) needle hydrophone, Ms Muller, Germany)inside the test tube was 60 5 per cent bar. Thetypical signature of the shock wave loading of themicrofuge tube is shown in Fig. 4. It is interestingto note here that the high pressure pulse of 60 baramplitude lasts for only 6s.

Exhaustive experimentation has been carried outto standardize the gene transformation protocols. Inthe beginning due to overdose, the bacterial cells werekilled after exposure to shock waves. The DNA trans-formation efficiency is also measured and comparedwith one of the standard methods of gene transforma-tion and the results are satisfactory as seen in Fig. 5.Using this method both E. coli and Agrobac. cells [9]have been successfully transformed. Efficacy of theshockwave transformed Agrobacterium in inducinginfection and expression of gene of interest (Gus gene)has also been confirmed by transient gene expressionassay. The interested readers can see references [8] and[9] for the details on the standard cell preparation andtransformation protocols.

It is likely that the exposure of shock waves tempo-rally enhances the cell membrane permeability [10, 11]

Fig. 4 Typical variation of the overpressure profile mea-sured using a needle hydrophone, inside thetest tube filled with the bacterial cells and thenaked plasmid DNA during the cell transforma-tion experiments. The bottom-most portion ofthe test tube was placed at a distance of 1 mmfrom the electrode tip


578 G Jagadeesh

Fig. 5 The DNA transformation efficiency obtainedfrom present experiments in comparison to theone of the conventional KCM (potassium, chlo-rine, and magnesium) method of bacterial celltransformation

thus enabling transformation. However, the actualmechanism of shock wave assisted Agrobacterium celltransformation needs to be clearly understood. Thetechnique proposed in this paper holds potential forintroduction of different macromolecules includingDNA in to different cell types. Currently efforts arefocused on commercially viable prototype building,testing followed by commercialization.

2.2 Preservative impregnation in bamboo usingvertical shock tube

A number of wood preservatives (chemical formula-tions toxic to wood decay/destroying organisms likefungi, wood destroying termites, marine borers etc.)and wood impregnating techniques are currently inuse for improving bio resistance of timber and bam-boo and thereby enhancing service life for differentend uses. However, some species of tropical hard-woods and many species of bamboo are difficult totreat, posing technical problems. Bamboo can grow inmost places; it is nutritious, checks soil erosion, con-serves moisture, repairs degraded land, and sequestercarbon and are useful against global warming. It hasgot 1500 recorded uses, can replace timber, steel, plas-tic, even liquor, and wine and estimated to provide8.6 million jobs in the India, with 136 species, has therichest bamboo resources after China.

In this backdrop, a collaborative research pro-gramme was initiated between the Indian Insti-tute of Science and the Institute of Wood Scienceand Technology, Bangalore, to develop and test a

new injection (water-soluble preservatives) systemfor bamboos using shockwaves. The main focus ofthe present study is in developing a commerciallyviable preservative injection system for treating bam-boo. Then the obvious question is why bamboo?Bamboo is regarded and promoted as an economi-cal substitute for conventional wood especially in theunder-developed regions of the world. Bamboos aretall, arborescent grasses belonging to the family Bam-buseae. However, in actual applications, bamboo mayreadily be damaged and destroyed by fungi, insects,and marine borers.

The conventional methods of treatment of bam-boo are pressure, hot, and cold treatments, sap dis-placement method and Boucheri processes. Theseprocesses, however, have their own limitations. Drybamboo is not amiable to preservative treatment. Theouter skin comprises of high silica content, therebyforming a good raincoat that prevents both insectsas well as preservative from entering the culm. Theinner part is covered with a waxy layer that is imper-meable as well. Therefore, the preservative can enteronly through the conducting vessels, which are notmore than 10 per cent of the cross-section. Hence,a new approach in treating bamboo has been envis-aged to get deeper penetration of the preservative forbetter service life. In case of timber, preservative is car-ried out nearly always on sawn timber. As a result ofsawing, numerous vessels and cells open up, consider-ably easing the penetration of any preservative. Also,timber has rays that provide cross sections betweenthe vessels. Unfortunately, these structural features arenot present in bamboo and hence they offer consider-able resistance to deep penetration of preservatives.Recently [12] a new shock wave assisted preservativeimpregnation technique was developed to push water-soluble preservatives into bamboo wood samples inthe laboratory.

A vertical shock tube (internal diameter, 50 mm;wall thickness, 12 mm) with 1.5 m driver and 2 mdriven sections separated by a metallic diaphragmhas been built for carrying out the preservative injec-tion experiment. Figure 6 shows the schematic of thevertical shock tube in the Shockwaves Lab in IISc,Bangalore. The water-soluble CCA (copper-chrome-arsenic) solution (4 per cent) is filled up to half-meterlength in the driven section tube before the exper-iment. Samples of Dendrocalamus strictus species(30 2.5 1.00 cm3) prepared from defect-free culmsof dry bamboo is fixed to end flange of the shocktube. The entire bamboo test specimen is immersedin the CCA preservative solution. Helium is used asthe driver gas and 1.5 mm thick metal diaphragmsare used for generating the shockwaves. The sam-ples are exposed to 30 5 per cent bar overpressurefor about 300 microseconds in the shock tube. Eachsample is subjected to repeat (three shots) shockwave



Fig. 6 Schematic diagram of a vertical shock tube facilityin IISc that was used for preservative impregna-tion studies into bamboo samples

loading during the preservative injection studies. Theexperimental samples are divided into three groups,each comprising six samples of bamboo. Three differ-ent treatment techniques like pressure treatment, hotand cold processes, [13, 14] and shockwave assistedtreatment have been carried out to estimate the level ofpenetration and the retention of the chemical preser-vative in the bamboo specimen. Figure 7 shows theamount of preservatives retained in bamboo sam-ples after shock wave treatment. Also shown in thesame graph are the preservative retention obtainedfrom conventional methods. Clearly the shockwaveassisted preservative injection system appears to bemore efficient compared to the conventional methods.The average data on treating with CCA preservativeis also recorded in all the split bamboo samples. Theabsorption, penetration, and retention in the treatedsamples are measured and the chemical analysis of thesample has been recorded in all the treatment meth-ods (Table 1). Further, the amount of time involved inthe treatment is only about 10 min including the timerequired for changing the diaphragm during the testswhereas time involved up to 3 h in conventional treat-ment systems. Although, not shown here, when thebamboo samples are subjected to single shot shock-wave loading, the results were only comparable toconventional technique and in some cases deep pene-tration was not possible. Shock waves are compressivein nature.

Recently [15], a new shock wave assisted diaphragm-less shock wave reactor was built to treat vatta wood

Fig. 7 The amount of copperchromearsenic preser-vative retained in the wood samples after shockloading. Also shown in this graph are the resultsobtained from preservative impregnation studiesusing conventional methods

Table 1 The tabulated results from the chemical analysisof the bamboo samples after the preservativeinjection by different methods

Density of chemical (kg/m3)

Shockwave Pressure Hot and coldChemical treatment treatment process

Chromium 10.31 6.874 2.75Copper 7.9 4.812 3.78Arsenic 0.9 2.13 0.68

slats that are used to make pencils. Figure 8 showsthe photograph of the pencils manufactured usingthe wood treated with shock waves. It is anticipatedthat the new method of preservative impregnationwill result in appreciable reduction in the produc-tion cycle time in the pencil manufacturing industry.It appears that the permeability of the bamboo sam-ples is enhanced because of repeated shock propa-gation through the specimen. Hence the preservativeis able to penetrate through the outer hard skinthereby facilitating better retention of the chemicalafter the treatment. Currently further targeted stud-ies are underway to confirm the actual mechanism ofshock wave assisted liquid preservative impregnationinto wood.


580 G Jagadeesh

Fig. 8 Pictorial view of the pencils made from thevatta wood slats that were treated in the shockwave reactor. The water-soluble preservative wasimpregnated in these wood slats using the newvertical diaphragmless shock wave reactor

2.3 Sandal oil extraction enhancement usingshock waves

India is a virtual treasure house to many rare and usefulspecies of wood. Sandalwood (Santalum album L.)is one such indigenous species found in abundancein the southern part of the Indian peninsula, widelyused for variety of pharmaceutical and medicinalapplications. The principal product extracted fromthe heartwood of the sandal tree is the oil, popularlyreferred as the East Indian sandalwood oil. Heartwoodfrom sandal trees upon distillation yields the oil that ischaracterized by a unique long-lasting characteristicaroma, and as a result it is also used in the manu-facture of variety of perfumes and cosmetics. Sandaloil has earned a prominent position in incense sticks,cosmetics, fragrance, and soap industries. It is alsofound useful in medicine as an antiseptic, antipyretic,diuretic, expectorant, treatment of bronchitis, and uri-nary infections. However, the use of sandal oil as a basein perfume manufacturing has far outweighed its usein medicine. By itself it is a mild, long-lasting sweetperfume, but the industry finds that it can blend wellwith other perfumes and does not impart its fragrancewhen used as a base [15].

Steam distillation is commonly employed for bothestimation as well as extraction of sandalwood oil. Insteam distillation, at least 50 g of heartwood powder isrequired for estimating the amount of oil in a givensample and this invariably results in considerabledamage to the tree. Recently Arun Kumar et al. [16]have also developed a non-destructive and easiermethod to estimate the oil content in sandalwoodin the laboratory. However, this hexane solvent-basedextraction process typically extends up to 18 h. In thisbackdrop, a new shock wave assisted oil extractionmethod is developed [17], which will not only increase

Fig. 9 The schematic diagram of the diaphragmlessshock tube facility used for sandal oil extractionenhancement studies

the commercial yield of the oil but at the same timesubstantially reduce the extraction time scales.

Figure 9 shows the schematic of the experimen-tal set-up. The cylindrical samples (diameter, 2.5 mm;length, 25 mm) are attached to the end flange hav-ing 50 mm constant area diaphragmless shock tube.A fast acting pneumatic valve is used to generate shockwaves and the sandalwood specimen is subjected tohigh pressure conditions (15 5 per cent bar) at theend wall of shock tube for about 1 ms. After the exper-iment, the samples are removed from the shock tubefor further extraction of oil using solvent extractiontechnique. Then slightly burnt aroma emanated fromthe wood samples. Although, electron spectroscopyfor chemical analysis (ESCA) not described here studies indicate the formation of silicon in the samplesexposed to shock waves. Further studies are under-way to understand the detailed chemistry duringinteraction of shock wave with sandalwood.

It is observed (not shown here) that both the rate andquantity of oil extracted from the sandalwood speci-men exposed to shock waves is clearly higher than therespective control specimen in all the samples testedduring the course of the study [17]. The amount ofoil extracted in different sandalwood samples drawnfrom different trees after shock wave loading showsan increase in the range of 4.56 to 58.51 per cent com-pared to the oil extracted from samples which were notexposed to shock waves. It is also interesting to notethat the rate of oil extraction in the samples exposedto shock waves is substantially enhanced during theinitial 30 min of the extraction process compared non-destructive oil extraction techniques. However, therate of extraction remains more or less the same forthe subsequent time interval across the treated andcontrol samples.

The scanning electron micrographs (Fig. 10) revealthat there is a change in the physical structure in caseof samples exposed to shock waves. The study furtherrevealed warty structures on the surface of the cross-section in addition to micro-fissures and cracks in theradial direction. These changes can be attributed tothe compressive effect in the sandalwood specimen



Fig. 10 The scanning electron microscope image of thesandalwood samples before and after shockwave exposure. The microfissures in the woodsamples exposed to shock waves are clearly seenin these microscopic images

exposed to shock waves. The interior oil globulesmight have been ruptured bringing the oil to the sur-face. Subsequently these samples when immersed insolvent might have extracted more oil than the non-destructive sandal oil extraction technique. However,more studies are necessary to understand the fun-damental effects of shock wave interaction on thewood anatomy. Further, gas chromatography (GC)(AIMIL NUCON GC 5500) studies using diethylene gly-col succinate (DEGS) column (stainless steel) underisothermal conditions (160 C oven temperature) havebeen carried out to check whether the quality of san-dal oil extracted is affected due to shock wave loading.The constituents (not shown here) of the sandal oilextracted are compared between exposed and con-trol core samples, showed very little variation in theintensity of the peaks observed (santalol) in the sam-ple exposed to shock waves and the control specimen.This is a clear indicator that there is virtually no effectof shock wave loading on the quality of the sandal oilextracted.

The results from the study indicates that both therate of extraction as well as the quantity of oil obtainedfrom sandalwood samples exposed to shock waves arehigher (1540 per cent) compared to non-destructiveoil extraction methods. The squeezing of the inte-rior oil globules in the sandalwood specimen due toshock wave loading appears to be the main reasonfor enhancement in the oil extraction rate. This isconfirmed by the presence of warty structures in thecross-section and micro-fissures in the radial direc-tion of the wood samples exposed to shock waves inthe scanning electron microscopic studies.

2.4 Shock wave-assisted dust removal from siliconwafer surface

Micron and sub-micron particulate contamination isbelieved to be responsible for more than 80 per centyield loss in semi-conductor industries. With the evershrinking device sizes in the micro-electronic indus-try, there is an urgent need to come up with moreeffective dry cleaning techniques. This study describesthe development of a novel shock wave assisted tech-nique [18, 19] for removing sub-micron dust particlesfrom silicon wafer surfaces. Figure 11 shows the photo-graph of the high-speed rotor with grooves along withthe pneumatic fixtures for mounting the silicon wafersfor cleaning experiments. The depth of the angulargroove is 5 mm and three such grooves are made onthe rotor at 120 apart. Various types (not discussedhere) of surface corrugations have been tried to arriveat the best possible geometric configuration for dustremoval experiments. Silicon wafers are mounted inthe vicinity (12 mm stand-off distance) of a high-speed (60 000 r/min) corrugated cylinder (diameter,140 mm; length, 45 mm). The high strength aluminiumalloy rotor is powered by a bi-directional 3-phase alter-nating current (AC) induction water-cooled motor thatoperates at 240V and maximum power of 5 kW. Therotor itself is supported on both the sides with ceramicbearings with maximum permissible axis vibration ofabout 30 microns at peak speed. This is the most crit-ical part of the device since the silicon wafer surfacesare mounted very close to the rotating surface. Provi-sion is made to generate a sonic jet coming from theaxial direction in between the stationary wafer surfaceand the spinning rotor.

In this study, sub-micron size dust removal exper-iments have been carried out by using the corru-gated cylinder spinning at supersonic edge speeds(380 m/s) in the vicinity of 80 mm diameter silicon

Fig. 11 Photograph of the high-speed rotor deviceused for shock-wave-assisted dust removal fromsilicon wafer surfaces


582 G Jagadeesh

wafer surfaces. The sub-micron particles (tungstenand aluminium dioxide) of known size are used tocontaminate both plain as well as patterned (with cir-cuit etching) silicon wafer surface in this study. Theparticles are deposited on the wafer by preparing asolution of known quality of particles in anhydrousalcohol. The alcohol evaporates after a short periodleaving behind a stain of the particle clusters on thewafer surface. Microscopic images of the surface of thewafer are taken before and after the cleaning process.Figure 12 shows the results from the cleaning experi-ments carried out using 0.7m tungsten particles. Thephotographs clearly show that the micron size parti-cles have been removed using the present techniquein both plain and patterned silicon wafers. In prac-tice, it is the dust on the wafer surface that originatesmostly from the deposition of silicon dioxide particlesduring the circuit etching process carried out in cleanrooms. However, efforts to remove 0.10m aluminium

Fig. 12 A microscopic image of a portion of the siliconwafer surface subjected to shock wave load-ing. The removal of tungsten particle dust(0.7 micron diameter) deposited before shockwave loading is clearly seen from these images.The rotor speed was 45 000 r/min at a stand-offdistance of 1 mm between the silicon wafersurface and rotor, with the sonic argon jetimpinging on the wafer surface

dioxide particles deposited on the wafer surface yieldonly partial results. The microscopic adhesive forceslike van der Waals, covalent, and the capillary forces,between the particle and the wafer surface are rathersubstantial with the decrease in the particle diame-ter which complicates the task of removing them fromsurface. In any case these are still early days before thedevice is integrated to the assembly lines in the micro-electronic industry. Issues such as the role played bythe jet in removing the dust from the surface, themacro and micro characteristics of the complex fluidstructure interaction in the narrow gap between therotor and the wafer surface, and the identification ofcritical control parameters influencing the cleaningprocess have to be resolved in future studies.

3 CONCLUSIONS

To the researchers in the area of compressible flows,occurrence of shock waves is nothing new. However,utilizing the instantaneous increase in pressure andtemperature behind a propagating shock wave in anymedium, it is indeed possible to come up with inter-esting industrial applications of shock waves. In thispaper, four such industrial applications developedin the Shock Waves Laboratory in IISc have beenreviewed. Using shock waves generated in an under-water shock wave generator, the desired plasmid DNAhas been successfully injected intoE. coli andAgrobac-terium cells. With the help of vertical shock wavereactor, water-soluble chemical preservative (copperchromearsenic) has been successfully injected tosamples of bamboo. Utilizing the same technique,shock wave-based preservative impregnation reactorhas been developed for pencil manufacturing indus-try. Subjecting the samples of sandalwood to shockwave loading in the horizontal diaphragmless shocktube, resulted in drastic reduction (40 per cent) in thetime required for oil extraction. Further, a new shockwave assisted technique for micron-size dust removalfrom silicon wafer surfaces has been developed incollaboration with the Interdisciplinary Shock WaveResearch Center, Tohoku University, Sendai, Japan.The strong vortex field generated behind the Machreflection of a shock wave has been used to removemicron size dust particles from the surface of siliconwafers.

ACKNOWLEDGEMENTS

The author wishes to place on record his thanks toThe Director, Inter-disciplinary Shock Wave ResearchCenter, Tohoku University, Japan, for providing himan opportunity to work in the Center during his sab-batical. The author owes his gratitude to the scientistsat the Department of Crop Physiology for all the help



in the cell transformation experiments. The authorwishes to thank the Director and the scientists ofInstitute of Wood Science and Technology, Bangalore,India, for providing all the help in the experiments. Theauthor would also like to thank the staff and studentsof Shock Waves Laboratory in IISc for the help duringthe experiments.

REFERENCES

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4 Kawahara, M., Kambe, K., Kurosu, S., Orikasa, S.,and Takayama, K. Extracorporeal stone disintegrationusing chemical explosive pellets as an energy source ofunderwater shock waves. J. Urol., 1986, 135, 814817.

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11 Lauer, U., Burgelt, E., Squire, Z., Messmer, K., Hof-schneider, P. H., Gregor, M., and Delius, M. Shock wavepermeabilization as a new gene transfer method.M.GeneTher., 1997, 4(7), 710715.

12 Rao, K. S., Lal, R., Ravikumar, G., and Jagadeesh, G.A new shock wave assisted wood preservative injectionsystem. In Proceedings of the 24th International Sympo-sium on Shock Waves, Beijing, China, 2004, vol. 2, pp.12591264.

13 Richardson, B. A. Wood preservation, 1978 (TheConstruction Press, London).

14 Jagadeesh, G. Application of shockwaves in pencilmanufacturing industry. In Proceedings of the 26thInternational Symposium on Shock Waves, Gottingen,Germany, 2007 (in press).

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17 Arun Kumar, A. N., Srinivasa, Y. B., Ravikumar, G.,Shankaranarayan, K. H., Rao, K. S., and Jagadeesh, G.A new shock wave assisted sandalwood oil extractiontechnique. In Proceedings of the 24th InternationalSymposium on Shock Waves, Beijing, China, 2004, vol.2, pp. 12351239.

18 Takayama, K., Jagadeesh, G., and Shibasaki, S. High-speed rotor device for removal of particles from solidsurfaces using shock waves. Japanese Pat. 3445982, 2003.

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