JOURNAL OF APPLIED PHYSICS 101, 123302 共2007兲

Characteristics of atmospheric-pressure, radio-frequency glow discharges operated with argon added ethanol Wen-Ting Sun, Guo Li, He-Ping Li,a兲 Cheng-Yu Bao, Hua-Bo Wang,b兲 and Shi Zeng Department of Engineering Physics, Tsinghua University, Beijing 100084, People’s Republic of China

Xing Gao School of Public Health and Family Medicine, Capital University of Medical Sciences, Beijing 100069, People’s Republic of China

Hui-Ying Luo Beijing Center for Diseases Control and Prevention, Beijing 100013, People’s Republic of China

共Received 4 December 2006; accepted 4 May 2007; published online 20 June 2007兲 Rf, atmospheric-pressure glow discharge 共APGD兲 plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show that the breakdown voltage can be reduced significantly when a small amount of ethanol is added into argon, probably due to the fact that the Penning ionization process is involved, and a pure ␣-mode discharge can be produced more easily with the help of ethanol. The uniformity of the rf APGDs of pure argon or argon-ethanol mixtures using bare metallic electrodes is identified with the aid of the intensified charge coupled device images. © 2007 American Institute of Physics. 关DOI: 10.1063/1.2748430兴 I. INTRODUCTION

Although low-pressure plasmas have found their wide applications in the last few decades, operating at reduced pressures requires expensive and complicated vacuum system which results in the high capital costs, the size limitations on the treated objects, the complex robotic assemblies used to shuttle materials in and out of vacuum chamber, etc.1 In recent years, different kinds of atmospheric-pressure nonequilibrium discharges 共APNEDs兲, such as the dielectric barrier discharge 共DBD兲 plasma,2 the plasma needle,3 the cold arc-plasma jet,4 the one atmosphere uniform glow discharge plasma 共OAUGDP兲,5 the surface-wave discharge,6 the microhollow cathode discharge,7 the radio-frequency atmospheric-pressure plasma jet,8,9 etc., are often covered under the rather broadly used term atmospheric-pressure glow discharge 共APGD兲. But some of them cannot be directly connected to the standard glow discharges. The common feature in all these discharge plasma sources is that they attempt to produce nonequilibrium 共low temperature兲 plasmas at atmospheric pressures. So, in this paper, the term glow discharge symbolizes nonequilibrium plasma as a general terminology. Among different kinds of APGD plasma sources, the APGD plasmas using bare metal electrodes driven by rf power supply developed in recent years have attracted much attention of the researchers.10–15 Besides the removal of the vacuum chamber, the breakdown voltage of the rf APGD plasmas with bare metal electrodes can be reduced significantly compared with atmospheric-pressure Author to whom correspondence should be addressed; FAX: ⫹8610 627829990; electronic mail: [email protected] b兲 Present address: Infinova 共Shen Zhen兲 Ltd., Shen Zhen 518053, Guangdong Province, People’s Republic of China. a兲

0021-8979/2007/101共12兲/123302/6/$23.00

DBDs resulting from the elimination of the dielectric共s兲 covered on the electrodes or placed between electrodes in DBDs.1 With the foregoing outstanding features, the rf APGD plasmas using bare metal electrodes have shown bright prospects to potentially replace low-pressure discharge devices in some existing applications and to create other applications in future, such as plasma-aided etching in microelectronic industry,16,17 plasma-enhanced chemical vapor deposition of silicon nitride or silicon dioxide films,18–20 decontamination of chemical and biological warfare 共CBW兲 agents,21 decommissioning of radioactive and chemical waste,22 inactivation of micro-organisms,23,24 graffiti removal, car wash,25 and so on. Usually, in the rf APGD plasmas using bare metallic electrodes, the primary working gas is helium, into which a small fraction 共0.5%–3%兲 of reactive gases 共e.g., O2, CF4, water vapor, etc.兲 may be added in order to generate a flux of chemically active species.8,16–23,26–29 Although it is easier to obtain a uniform glow discharge with pure helium as the primary plasma-forming gas, the consumption of expensive helium increases the operation costs for this case. Recently, studies on the characteristics of rf APGD plasmas are reported with pure argon30 or argon-oxygen 共1% in volume兲31 as the plasma-forming gas. Although the operation costs can be reduced using argon, instead of helium, the breakdown voltage for argon is much higher than that for helium.26,30 As is well known, the higher breakdown voltage may cause a rapid multiplication of electrons after breakdown and lead to the formation of streamers or a filamentary arc.26 In Ref. 32, it was also pointed out that it was difficult to initiate and maintain the stable, atmospheric-pressure rf ␣-mode glow discharge plasmas with argon due to the high breakdown

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FIG. 1. Schematic diagram of the experimental setup 共a兲, the coaxial-type plasma generator 共b兲, and the planar-type plasma generator 共c兲.

voltage. Therefore, it is necessary to study the discharge mechanisms of the rf glowlike discharge plasmas using bare metal electrodes under different operation conditions in order to achieve stable, uniform glowlike discharges using a variety of plasma working gases and at lower breakdown voltages. In this study, the discharge characteristics of rf APGDs, including the breakdown voltage of the gas, the relationship between the discharge mode after breakdown and the gap spacing, etc., are investigated with pure argon and argonethanol mixture as the plasma-forming gas and using bare metal electrodes. II. EXPERIMENTAL SETUP

A schematic diagram of the experimental setup is shown in Fig. 1共a兲. Two types of plasma generators are employed in this experiment as shown in Figs. 1共b兲 and 1共c兲, respectively. The coaxial-type plasma generator, as shown in Fig. 1共b兲, consists of two 95 mm long, coaxial, water-cooled copper electrodes. The inner diameter of the outer electrode, which is employed as the grounded electrode, is 19.2 mm, while the central electrode is rf 共13.56 MHz兲 powered with a diameter of 16.0 mm. Figure 1共c兲 shows the planar-type plasma generator which is composed of two 5 ⫻ 8 cm2 planar, bare, water-cooled copper electrodes, i.e., the rf powered top electrode and the grounded bottom electrode. Teflon spacers are used to seal the plasma generator on both sides and adjust the distance between the electrodes. The powered electrodes of the plasma generators are connected to the rf power supply through a matching network. The plasma-forming gas 共argon, or argon-ethanol mixture with argon passing through a homemade chamber in which the argon is mixed with ethanol兲 enters the discharge region, ionized between electrodes

under the applied rf electric field, and flows out of the generator. The concentration of ethanol in the argon-ethanol mixture is adjusted by controlling the number of the graduated cylinders placed in the chamber. A pipette with accuracy of 0.02 ml is used to measure the total consumed ethanol 共Vethanol兲 at a time interval ⌬t. If the argon flow rate is QAr, the ethanol concentration can be expressed as Cethanol = 共␳ethanolVethanol兲 / 共⌬tQAr兲 共mg/l兲, where ␳ethanol is the mass density of the ethanol. The rms values of the voltage and current are measured using a high voltage probe 共Tektronix P5100兲 and a current probe 共Tektronix TCP202兲, respectively, and recorded on a digital oscilloscope 共Tektronix TDS3034B兲. The discharge pictures are taken by a digital camera 共Fujifilm S5500兲 and an intensified charge coupled device 共iCCD兲 共Type DH734-18F-03/W/P43兲 camera, respectively. With the Andor iStar 734 iCCD, very short time acquisition 共down to 5 ns exposure time兲 of the discharge can be performed in order to detect the presence of streamers in the discharge gap. By removing the cameras, the spectra of the discharge are measured by a monochromator 共WDG30, Beijing Optical Instrument Factory, China兲 plus photomultuplier tube 共CRC131-01, Beijing Hamamatsu Photon Techniques Inc., China兲 system with wavelengths ranging from 200 to 800 nm. In this paper, for investigating the relationship between the gas breakdown voltage and the gap spacing, and also for taking the pictures using the iCCD conveniently, the planar-type plasma generator 关shown in Fig. 1共c兲兴 is employed, while other measurements are conducted using the coaxial-type plasma generator 关shown in Fig. 1共b兲兴 with constant gap spacing d = 1.6 mm.

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FIG. 2. 共Color online兲 I-V curves for pure argon and argon-ethanol rf APGDs using the coaxial-type plasma generator, QAr = 5.0 slpm.

III. EXPERIMENTAL RESULTS A. Electrical measurements

Similar to the rf capacitive discharges at intermediate pressure, the rf APGD can assume two different but stable operation modes, i.e., ␣ mode, which is sustained by volumetric ionization processes, and ␥ mode, in which ionization by secondary electrons from electrode surfaces is important.27,33 Secondary electron emission strongly influences the gas ionization in the ␥ mode discharge but matters little in the ␣ mode dishcarge.10 The two modes differ in the intensity and luminosity distribution along the discharge length. When the ␥ mode appears, it contracts so that the current density at the electrodes rises and the discharge column changes its shape radically at each electrode.33 In this experiment, due to the large area of the electrodes 共about 40 cm2 for both the coaxial-type and planar-type plasma generators兲, the ␥ mode discharge can only cover a small part of the electrodes due to the limitation of the maximum power output of the rf power supply used in this lab. But the ␣ mode discharge can cover the whole gap space. In this paper, we distinguish the two discharge modes by visual difference, i.e., there is a bright negative glow very close to both electrodes with a few filamentlike contracted positive columns for argon ␥ mode discharge. The similar results were also reported by Laimer et al.30 The measured current and voltage characteristics, i.e., the so-called I-V curves, of the discharge process for pure argon and argon-ethanol mixtures with different ethanol concentrations are shown in Fig. 2 for the case with the argon flow rate QAr = 5.0 standard liters per minute 共slpm兲. Figure 2 shows that for the discharge process with pure argon, the ignition occurs at point A with a rather high breakdown voltage 共566 V兲. After breakdown, the discharge voltage drops sharply to 134 V 共point B兲, and a uniform glow discharge operated in ␣ mode appears fully between electrodes with the power input of about 60 W. Then, with the increase of the discharge current 共B-C兲, the discharge voltage slightly increases, and the ␣-mode discharge is maintained. With the continuous increase of the discharge current, a ␥-mode discharge or arcing may occur after point C associated with larger rf power input. On the other hand, for the discharge processes with argon-ethanol mixtures, the ignitions occur with much lower breakdown voltages. The lowest breakdown voltage is 139 V for Cethanol = 0.7 mg/ l, while 166 and 170 V for Cethanol = 0.2 and 4.7 mg/ l, respectively, in

FIG. 3. 共Color online兲 Photographs of the discharge after breakdown using the coaxial-type plasma generator, QAr = 5.0 slpm, 共a兲 pure argon; 共b兲 argonethanol mixture 共Cethanol = 0.2 mg/ l兲.

this study. For all the cases with argon-ethanol mixture as the plasma-forming gas, the discharge voltages drop slightly after breakdown, and the uniform ␣-mode discharge only partially covers the electrodes due to the low power input 共about 30 W兲. Then, with the increase of the discharge current, the ␣-mode discharge region becomes larger and can cover all the electrode surfaces, accompanied with the increase of the discharge voltage. And similarly, as the discharge current is increased continuously, arcing or ␥-mode discharge usually occurs associated with the larger power input. The measurements presented in Fig. 2 are all repeated three times for the discharge processes with argon or argon-ethanol mixtures, and the standard deviations of the measured discharge voltages are all smaller than 9 V. It can be seen from Fig. 2 that with the help of ethanol, the breakdown voltage drops significantly compared with the case of pure argon discharge, i.e., the lowest breakdown voltage with the ethanol concentration 0.7 mg/ l is only ⬃1 / 4 of that at point A corresponding to the discharge with pure argon. In Ref. 30, it was reported that an ␣-␥ coexisting mode always occurs after breakdown. It is found in this study that ␣ and/or ␥ mode can appear directly after breakdown, depending on the gap spacing between electrodes, the matching network of the circuit, etc. It is also found that the ␣-mode discharge, instead of the ␣-␥ coexisting mode, can be achieved much more easily after breakdown for the argonethanol rf APGDs with bare metal electrodes. As seen in Fig. 3共a兲, for QAr = 5.0 slpm and power input Pin = 113 W, a ␥-mode discharge with several filamentlike columns coexists with a uniform ␣-mode discharge after breakdown. However, for the same argon flow rate, a pure ␣-mode discharge can be obtained after breakdown with the ethanol concentration 0.2 mg/ l, as shown in Fig. 3共b兲 at a much lower input power

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FIG. 4. 共Color online兲 Relationship between the breakdown voltage and the gap spacing with pure argon and argon-ethanol mixture using the planartype plasma generator, QAr = 5.0 slpm.

Pin = 28 W. And with increasing the input power, the pure ␣-mode discharge can cover the full space between electrodes. In order to study the influence of the gap spacing 共d兲 on the breakdown voltage 共Vb兲 and the discharge mode after breakdown, the planar-type plasma generator, as shown in Fig. 1共c兲, is employed in this study. Figure 4 shows that with constant argon flow rate QAr = 5.0 slpm 共1兲 for both cases with pure argon or argon-ethanol mixture as the plasmaforming gas, the breakdown voltages increase with increasing the gap spacing between electrodes; 共2兲 at the fixed gap spacing, the breakdown voltage for pure argon discharge is much higher than that for the case of argon-ethanol discharge; 共3兲 for argon-ethanol discharge, the critical value of the gap spacing between electrodes for obtaining a pure ␣-mode discharge after breakdown is ⬃2.5 mm, which is much larger than the corresponding value for the case of pure argon discharge 共⬃1.3 mm兲. When the gap spacing exceeds its critical value, a ␥-mode or ␣-␥ coexisting mode discharge may occur after breakdown.

FIG. 5. Variations of the breakdown voltage with different ethanol concentrations using the coaxial-type plasma generator, QAr = 5.0 slpm.

The relationship between the breakdown voltage 共Vb兲 and the ethanol concentration 共Cethanol兲 is also studied with the coaxial-type plasma generator in this paper. It is found that an optimum value of the ethanol concentration exists corresponding to the lowest breakdown voltage. As shown in Fig. 5, when the ethanol concentration is about 0.7 mg/ l, the lowest breakdown voltage appears in this study, while both lower and higher ethanol concentrations than this optimum value result in higher breakdown voltages. The similar phenomena are also observed by using the planar-type plasma generator. B. Discharge images

To identify the uniformity of the discharges with argon and argon-ethanol mixtures, the discharge images are taken in a short exposure time 共Tex = 10 or 30 ns兲 with the Andor iStar 734 intensified CCD camera, and also compared with the pictures taken by the digital camera 共Fujifilm S5500兲. In Fig. 6, the pictures listed on the left column, i.e., Figs. 6共a兲–6共d兲, are taken by the iCCD with a short exposure time

FIG. 6. 共Color online兲 Discharge images taken by the iCCD camera 关共a兲–共d兲兴 and the digital camera 关共e兲–共h兲兴 using the planar-type plasma generator, QAr = 5.0 slpm, d = 1.24 mm 共a兲 ␣-mode discharge of pure argon, Tex = 10 ns, Pin = 65 W; 共b兲 ␥-mode discharge of pure argon, Tex = 10 ns, Pin = 150 W; 共c兲 ␣-mode discharge of argon-ethanol mixture 共0.2 mg/ l兲, Tex = 10 ns, Pin = 80 W; 共d兲 ␣-mode discharge of argon-ethanol mixture 共9.5 mg/ l兲, Tex = 30 ns, Pin = 20 W; 共e兲 ␣-mode discharge of pure argon, Tex = 2.5 ms, Pin = 65 W; 共f兲 ␥-mode discharge of pure argon, Tex = 2.5 ms, Pin = 150 W; 共g兲 ␣-mode discharge of argonethanol mixture 共0.2 mg/ l兲, Tex = 2.5 ms, Pin = 80 W; 共h兲 ␣-mode discharge of argon-ethanol mixture 共9.5 mg/ l兲, Tex = 125 ms, Pin = 20 W.

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FIG. 7. 共Color online兲 Emission spectra of the excited argon and oxygen atoms with different ethanol concentrations, QAr = 5.0 slpm, d = 1.24 mm.

关Tex = 10 ns for Figs. 6共a兲–6共c兲 and 30 ns for Fig. 6共d兲兴, while their counterparts on the right column, i.e., Figs. 6共e兲–6共h兲, are taken by the digital camera with a longer exposure time 关 Tex = 2.5 ms for Figs. 6共e兲–6共g兲 and 125 ms for Fig. 6共h兲兴. In Figs. 6共d兲 and 6共h兲, the longer exposure time is employed compared with their counterparts because of the low emission intensity of the discharge with high ethanol concentration 共9.5 mg/ l兲. Figure 6 clearly shows the laterally uniform rf APGDs without any streamers. C. Spectroscopic measurements and discussions

In Ref. 34, the influence of the ethanol 共CH3CH2OH兲 on the behaviors of the electron and ion densities and distribution of metastable Ar* in flowing afterglow plasmas were investigated in the pressure range of 10– 100 Pa. It was indicated that a comparatively sharp increase in both electron and ion densities occurred when the titration vapor 共ethyl alcohol兲 was added into the plasma-forming gas 共argon兲 due to the Penning ionization Ar* + CH3CH2OH → B+1 + D1 + e,

共1兲

where B+1 and D1 represent the products of ions and neutrals, respectively, while e stands for the electrons.34 It was also indicated in Ref. 35 that the bands between carbon and hydrogen atoms in the alcohols could be broken in an argon surface wave sustained discharge at atmospheric pressure. Because the internal energy of the metastable Ar* 共⬃11.55 eV兲 is higher than the ionization energy of an ethanol molecule 共⬃10.47 eV兲,34 it is expected that the Penning ionization 共1兲 may also occur in the present argon-ethanol rf APGDs, which could lead to a great decrease of the breakdown voltage. The emission spectra of the discharges with different ethanol concentrations are performed by optical emission spectroscopy in this study. The excited argon atomic lines at 696.5, 707, 715, 727, 750, 763.5, and 772.4 nm 共Refs. 31 and 36兲 are depicted in Fig. 7 for the rf APGD plasmas with argon as the primary plasma-working gas. The corresponding spectra of hydroxyl 共OH兲 molecular band 共A2⌺+, ␷ = 0 → X2⌸, ␷⬘ = 0, 306– 310 nm兲37 under the same operation conditions are shown in Fig. 8. The OH molecular spectrum 共306– 310 nm兲 and the excited oxygen atom emission line

FIG. 8. 共Color online兲 Emission spectra of hydroxyl molecular 共OH兲 band with different ethanol concentrations, QAr = 5.0 slpm, d = 1.24 mm

共777 nm兲 are also seen in Figs. 7 and 8 even for the pure argon discharge. One of the reasons for this phenomenon is that the discharges are generated in ambient air.31,36 It can be seen from Figs. 7 and 8 that 共1兲 the introduction of the ethanol is one of the possible reasons which results in the production of the radical of hydroxyl 共OH兲 due to the Penning ionization process discussed above; 共2兲 the intensity of the hydroxyl band increases sharply at first with a small concentration of ethanol 共0.1 mg/ l兲, and then, with the further increase of the ethanol concentration, the intensity of hydroxyl band decreases; 共3兲 the emission intensities of the excited argon and oxygen atomic lines decrease with increasing the ethanol concentration. In Ref. 38, it was indicated that ionization through metastables was one of the important processes in increasing the plasma density; and the densities of the argon metastables 共Ar*兲 and electrons, as well as the optical emission intensities, decreased with the increase of N2 ratio in an argonnitrogen mixture at a low pressure range 共0.1– 2.0 Torr兲 due to the stepwise ionization and metastable pooling. In this study, the argon metastables 共Ar*兲 may play the similar role as that discussed in Ref. 38 in the discharge processes for the argon-ethanol rf APGDs due to the Penning effect 共1兲, since the emission intensities, including the optical emission intensity of argon metastables 共Ar*兲 at 696.5 nm,38 of the argonethanol discharges are lower than those for a pure argon discharge, as shown in Fig. 7. Because of the very complex chemical processes involved in the argon-ethanol plasma system, the deeper investigations on the discharge mechanisms and chemical reactions in the argon or argon-ethanol rf APGDs need to be conducted in future work. IV. CONCLUSIONS

In this paper, the discharge characteristics of the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes are investigated. The experimental results show that a small fraction addition of ethanol into argon can significantly reduce the breakdown voltage of the rf APGD plasmas generated between the bare metal electrodes, and make it easier to obtain more uniform glowlike discharges operated in ␣ mode after breakdown compared with

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the pure argon discharge, probably due to the Penning ionization process involved in the argon-ethanol rf APGDs. The uniformity of the rf APGDs with the pure argon or argonethanol mixture using bare metal electrodes is also identified by the iCCD images. Further studies concerning the influences of the ethanol on the discharge mechanisms in a rf APGD plasma with argon-ethanol mixture as the plasmaforming gas are necessary in future work. ACKNOWLEDGMENT

This work has been supported by the project sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry of China. The iCCD images presented in this paper were taken using the iCCD camera of the Plasma Lab, the Institute of Mechanics, Chinese Academy of Sciences. 1

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Characteristics of the Epic Hero
Basically, this means the hero has the potential for great deeds. ❖ The magnitude of these actions are well above and beyond what the commoner does. ❖ While most epic heroes are good, not all are. Trait 3: Great Warrior. ❖ Before the hero of an

GUIDED-WAVE CHARACTERISTICS OF PERIODICALLY ...
Introduction. The parallel-coupled microstrip line was extensively characterized in the past and has been gaining a wide application in the bandpass filter design ...

experiment_2 study of characteristics of strain ... - MOBILPASAR.COM
CRO. 1. 6. Breadboard. 1. 7. Connecting wires. As required. 8. Probes for CRO. 2. RC PHASE SHIFT OSCILLATOR. PROCEDURE. 1. Connect the components ...

Characteristics of Business Owners:2002 - Census Bureau
X. X. Majority interest owners. X. X. 48.9 .2. X. X. 39.2 .2. X. X. 63.1 .4. Equal interest owners. X. X. 29.0 .2. X. X. 26.5 .2. X. X. 32.5 .5. Nonmajority interest owners.

Emission characteristics of random lasers
A resonator with an amplifying medium embedded ... an individual spectrum with the ensemble-averaged spectrum that carries the signature of the gain profile.

Phenomenal characteristics of autobiographical memories for social ...
Previous studies failed to show clear differences between people with social phobia and non-anxious individuals regarding the specificity and affective intensity of their autobiographical memories for social events. However, these studies did not ass

Characteristics of Business Owners:2002 - Census Bureau
Bureau to take the economic census every 5 years, covering years ending in ''2'' .... the year. Receipts size and employment size are determined for the entire company. ...... lege, but no degree) that the owner(s) completed before establishing, ....

6 Characteristics of Life
6 Characteristics of Life. 1. Reproduction. 2. Grow and Develop. 3. Made of Cells. 4. Respond to a Stimulus. 5. Obtain and Use Energy. 6. Adapt and Evolve ...

Synthesis, spectral characteristics and electrochemistry of ... - Arkivoc
studied representatives of electron-injection/hole-blocking materials from this class is .... Here, the diagnostic peak comes from C2 and C5 carbon atoms of the.

Discharge characteristics of atmospheric-pressure ...
School of Public Health and Family Medicine, Capital University of Medical Sciences, Beijing 100069,. People's ... (Received 5 July 2006; accepted 29 August 2006; published online 19 October 2006) ..... D. Shim, and C. S. Chang, Appl. Phys.

The palynomorphological characteristics of Anthemis ...
with beautiful and attractive flowers. The article includes the palynomorphological study of the main members of genus Anthemis in Albania. In this article submitted comparative features of the species: Anthemis altissima ,. Anthemis carpatica, Anthe

Emission characteristics of random lasers
This claim was experimentally verified in a dye-scatterer ... spectrum with the ensemble-averaged spectrum that carries the signature of the gain profile.

Dynamic Characteristics of Prochlorococcus and ...
Received: 26 July 2001; Accepted: 7 January 2002; Online publication: 11 March 2002 ... Synechococcus abundance in the water, and the feeding rate showed a ...... Bank. Mar Ecol Prog Ser 192:103±118. 49. Sherr EB, Sherr BF, Paffenhofer ...

Characteristics of Performing Arts Talent.pdf
Page 1 of 1. Characteristics of Performing Arts Talent. Performing Arts. *exceptional coordination and sense of rhythm. *shows keen enjoyment of musical or ...

Dynamic Characteristics of Prochlorococcus and ...
... MA 02543, USA. Correspondence to: U. Christaki; E-mail: [email protected] ..... Linear regression models (continuous lines) were fit to the solid data points ...

Characteristics of Spatial Learners.pdf
There was a problem previewing this document. Retrying... Download. Connect more apps... Try one of the apps below to open or edit this item. Characteristics ...

Certain Characteristics of Unlicensed Tree Expert Companies ...
(69.91%) found to be advertising tree services online were unlicensed tree experts (UnLTEs). .... other records in the listing of over 1,400 UnLTEs be- ... online directories of Verizon and AT&T telephone listings is ..... fónicas en Internet.

Characteristics of Performing Arts Talent.pdf
*plays one or more musical instruments (or sings) with higher. than expected level of expertise. *makes up original work. *highly expressive in the area of ...

Photoluminescence Characteristics of Macroporous Eu ...
Mar 23, 2009 - Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University,. Higashihiroshima, Hiroshima 739-8527, Japan.

Characteristics of meteorological parameters ...
R. Gautam, G. Cervone, R. P. Singh,1 and M. Kafatos ... and r and E are constants. ..... Hong, X. D., S. W. Chang, S. Raman, L. K. Shay, and R. Hodur (2000),.