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electrically floating. Its temperature was monitored with a thermocouple probe connected to a digital thermometer. The reactor was vacuumed to a base pressure below 2.67 × 10 −3 Pa (2 × 10 −5 Torr) by a ULVAC Japan Ltd. (model YH− 500A) high vacuum system, and pure O2 was introduced to ensure a working pressure of 2 Pa (15 mTorr). The absolute gas pressure was monitored during the plasma discharge by a Baratron manometer and the base pressure was measured by an ion gauge. 2.3 Microbiological diagnostics The microbiological diagnostics undertakes with a review on the theoretical aspect of the inactivation process and tend to complete the definitions presented in the introductory part of the thesis. The methodology and materials needed for an accurate diagnostic and efficient detection of the bacteria inactivation are closing this section. 2.3.1 Theoretical description of bacteria inactivation The inactivation of a microorganism population is a statistical process [24, 25]. That is, it is impossible to predict when any of the microorganisms will die, knowing that the initial population N0 contains a sufficiently big number of indi- viduals such that the statistical methods to be applicable (i.e., N0 is large enough that the statistical variation in the inactivation rate will average out). Under 27
such circumstances, the inactivation process must be mathematically described in terms of probability of inactivation per unit time. If at the time t after the beginning of the inactivation process the number of still surviving microorganisms is N(t), andafterashorttimeinterval∆t, the number is N(t + ∆t), then the number of bacteria that died in the time ∆t is ∆N = N(t) − N(t + ∆t). (2.1) Consequently, the decrease of the number of surviving bacteria during ∆t will be −∆N. It is experimentally observed that for a given initial population of microorganisms, over short time intervals ∆t the speed of bacteria inactivation is constant N(t) − N(t + ∆t) r = lim = cst. (2.2) ∆t→0 ∆t For large bacteria population and very short inactivation times, the quantity N can be treated as a continuous one, from mathematical point of view. Expanding N(t + ∆t) in Taylor series and keeping only the linear terms, Eq. (2.2) becomes: r = lim ∆t→0 N(t) − [N(t)+ dN ∆t + ...] dt ∆t ∼ dN = − . (2.3) dt Equation (2.3) showsthat,ifindt the number of inactivated bacteria is dN, then in 2dt the number of inactivated bacteria will be 2dN. Another experimental observation is that the number of inactivated bacteria 28
Page 1 and 2: PLASMA STERILIZATION USING LOW PRES
Page 3 and 4: my appreciation especially for the
Page 5 and 6: Iis ion saturation current [µA] t
Page 7 and 8: CONTENTS 1 PRINCIPLES OF SURFACE DI
Page 9 and 10: 4 EFFECTS OF LOW TEMPERATURE PULSED
Page 11 and 12: and intuited to bring new important
Page 13 and 14: Figure 1.1: Schematic representatio
Page 15 and 16: Table 1.1: Common disinfection and
Page 17 and 18: the radiation energy is resonantly
Page 19 and 20: ers of heat, optical radiation and
Page 21 and 22: Table 1.2: Main plasma sources used
Page 23 and 24: microorganism population as a respo
Page 25 and 26: UV Photon Before After DNA Figure 1
Page 27 and 28: to sterilize medical tools, but the
Page 29 and 30: sented by both theoretical and expe
Page 31 and 32: Plasma Sterilization Using Low Pres
Page 33 and 34: Figure 2.1: Experimental set-up. MB
Page 35: Figure 2.3: Electronic circuit of t
Page 39 and 40: ment time t is N = N0e −αt ≡ N
Page 41 and 42: shows the number of the viable micr
Page 43 and 44: has n −1 0 > 281.25 µm 2 availab
Page 45 and 46: 1 st 2 nd ( I) TNTC (II) TNTC (III)
Page 47 and 48: U LC blocking filter 19.74 pF 20.24
Page 49 and 50: Figure 2.8: Experimental set-up use
Page 51 and 52: the reactive species from plasma ar
Page 53 and 54: Temperature measurement Relative in
Page 55 and 56: MR MP SH Figure 3.2: Experimental a
Page 57 and 58: a fast temperature increasing rate.
Page 59 and 60: D h (min) 10 3 10 2 10 1 10 0 100 2
Page 61 and 62: MR QP SH Figure 3.6: Experimental a
Page 63 and 64: The contribution of photons and hea
Page 65 and 66: D (min) 10 3 10 2 10 1 10 0 Dν D h
Page 67 and 68: N/N 0 (%) 10 2 10 2 10 2 10 2 10 2
Page 69 and 70: D (min) 10 2 10 1 10 0 D h+ν+p D h
Page 71 and 72: holder is mainly given by particle
Page 73 and 74: 3.5 Power sensitivity of spore inac
Page 75 and 76: If for a reference treatment temper
Page 77 and 78: of the sample was achieved. Moreove
Page 79 and 80: microorganisms were disposed in mon
Page 81 and 82: The pulse period covered a wide int
Page 83 and 84: in chapter 2. The treatment time of
Page 85 and 86: 4.2.2 Injected RF power In order to
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ton =500µs, and the duty cycle was
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T ( 0 C) 120 100 80 60 40 20 I 0 5
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N/N 0 (%) 10 2 10 2 10 2 10 1 10 1
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elow 70 ◦ C. 3. Increasing the in
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the second phase of the inactivatio
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k 1, 2 (min -1 ) 1.2 1.0 0.8 0.6 0.
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I (arb. unit) 140 120 100 80 60 40
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I (arb. unit) 5 4 3 2 1 0 0.000 0.0
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I > (arb.unit) 1.0 0.9 0.8 0.7 0.6
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shown in Fig. 4.14. It can be seen
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I is (mA) 0.25 0.20 0.15 0.10 0.05
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value. When ton has been kept const
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survival curve characteristics were
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of the effects produced by differen
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solutely necessary for a profound u
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Conferences 1. Bacillus spores ster
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[9] W. A. Rutala, D. J. Weber, J. H
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[34] J. H. Young: Sterilization wit
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[57] M. K. Boudam, M. Moisan, B. Sa
Page 125 and 126:
[79] J. Schneider, K. M. Baumgartne
Page 127 and 128:
[100] S. Villeger, S. Cousty, A. Ri
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