J W Mcbride

E M Yunus

S M Spearing

Improving the contact resistance at low force using gold coated carbon nanotube surfaces

Keywords: . Contact force, contact resistance, carbon nanotubes, and Au/multi walled carbon nanotubes. B

Investigations to determine the electrical contact performance under repeated cycles at low force conditions for carbon-nanotube (CNT) coated surfaces were performed. The surfaces under investigation consisted of multi-walled CNT synthesized on a silicon substrate and coated with a gold film. These planar surfaces were mounted on the tip of a PZT actuator and contacted with a plated Au hemispherical probe. The dynamic applied force used was 1mN. The contact resistance (R c ) of these surfaces was investigated with the applied force and with repeated loading cycles performed for stability testing. The surfaces were compared with a reference Au-Au contact under the same experimental conditions. This initial study shows the potential for the application of gold coated CNT surfaces as an interface in low force electrical contact applications.

Introduction

This paper presents a study of electrical contact between surfaces under low dynamic force conditions, typically 1mN. Such conditions are relevant to a number of microcontact applications, for example MEMS relay devices.

There are a number of potential materials commonly used for this application including gold, palladium and platinum [START_REF] Coutu | Selecting Metal Alloy Electric Contact Materials for MEMS Switches[END_REF]. The weakness of such materials is that they are relatively soft and wear easily. Other materials which are of interest on MEMS relay's micro-contact include silicon carbide and diamond films. Both have high moduli but low electrical conductivity. The latter makes them unsuitable for electrical contact applications. There have been attempts to increase the conductivity. When doping SiC film with NH3 the resistivity drops to 1 x 10 -4 Ωm [START_REF] Gao | High Modulus Polycrystalline 3C-SiC Technology for RF MEMS[END_REF] and doping DLC with ruthenium the resistivity drops to 1x10 -5 Ωm [START_REF] Lian | Ru-doped Nanostructured Carbon Films[END_REF], however, both materials still have a high resistivity compared to gold and even gold alloys (for example Au-6.3% Pt has a resistivity of 7.17 x 10 -8 Ωm) [START_REF] Coutu | Selecting Metal Alloy Electric Contact Materials for MEMS Switches[END_REF].

A carbon nanotube (CNT) coated surface has potential as a material for MEMS relay applications specifically as a contact material because of its excellent mechanical and electrical properties. An experiment has been performed [START_REF] Tzeng | Electrical contacts between carbon-nanotube coated electrodes[END_REF] to measure the contact resistance, R c between CNT coated electrodes in ambient air and in a vacuum. The author concluded that the contact resistance, R c was found to be much lower in ambient air (~160 Ω) than in vacuum (>4kΩ). In a more recent experiment [START_REF] Yaglioglu | Method of characterizing electrical contact properties of carbon nanotube coated surfaces[END_REF], Au contacts with a substrate coated with tangled single walled carbon nanotubes were investigated. The authors concluded that a tangled Single Walled Carbon Nanotube (SWCNT) film against an Au coated surface has a better performance than two contacting tangled films.

The following mechanical properties have been determined; CNTs tensile strength of up to 63 GPa has been measured [START_REF] Yu | Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load[END_REF]. Experiments using an atomic force microscope were performed to measure the elastic modulus and bending strength of individual, structurally isolated, multi-wall carbon nanotubes and indicated values of 1.26 TPa and 14.2 GPa [START_REF] Wong | Nanobeam Mechanics: Elasticity, Strength, and Toughness of Nanorods and Nanotubes[END_REF] respectively. Experiments were also conducted on CNTs using a nano-indentation apparatus and values were obtained for the bending modulus; 1.24 TPa, axial modulus; 1.23 TPa and wall modulus; 5.61 TPa [START_REF] Qi | Determination of Mechanical Properties of Carbon Nanotubes and Vertically Aligned Carbon Nanotube forests using Nanoindentation[END_REF]. Another report shows that CNT's have an elastic modulus greater than 1 TPa [START_REF] Thostenson | Advances in the Science and Technology of Carbon Nanotubes and their Composites: A review[END_REF] compared to diamond, which has a modulus of 1.2 TPa.

In terms of its electrical properties, it is calculated that a 4-10 μm long SWCNT with a diameter of 1.2nm has a resistivity of 0.88 x 10 -8 Ωm and is thought to exhibit ballistic electrical conduction. The calculation is performed using the theory of ballistic conductors and it is assumed that the CNT is defect-free. In addition, if a CNT were to be filled with metal, to form a composite its resistivity would fall to 0.35 x 10 -8 Ωm [START_REF] Hjortstam | Can we achieve ultra-low resistivity in carbon nanotubebased metal composites?[END_REF]. The mechanical and electrical properties are therefore potentially comparable to diamond and gold respectively, however, as yet no experiments have been reported on CNT metal composites for micro-contact applications. In the present work a novel approach is used in which a CNT "forest" is over coated with gold, in order to provide a high conductivity surface layer with a compliant under layer.

In previous work a modified nano-indentation apparatus [START_REF] Yunus | The Relationship between Contact Resistance and Contact Force on Au coated Carbon Nanotubes surfaces[END_REF] was used to determine the contact resistance, R c , as a function of contact force and load cycling up to ten load cycles. These initial results showed that the performance and contact resistance of Au-Au/MWCNT contact pairs is comparable to Au-Au contact pairs and during ten load cycles of Au-Au/MWNT contact pair shows stable and constant contact resistance. The contact resistance of the Au-Au/MWCNT is typically 0.5Ω at 1mN. This compares favorably with commercial MEMS relays where 1.5Ω is a common contact resistance. In this study a purpose built test system is used to investigate the dynamic performance of the surfaces under dry circuit conditions.

Material preparation

In the present study two contact pairs have been investigated; Au to Au and Au to Au/multi walled carbon nano-tubes (MWCNTs) composite. The geometry selected is a 2mm diameter hemisphere contacting a flat surface. In all cases the hemisphere consists of a stainless steel base, sputter coated with Au, ~500 nm thick, with surface roughness Ra≈400nm. In the Au to Au case (Sample 1), the flat surface is a silicon (Si) substrate (~2mm by 7mm), sputter coated with Au ~500 nm, with a surface roughness Ra≈30nm.

For the Au to Au/MWCNT case (Sample 2), a "forest" of MWCNTs is grown on the Si wafer using thermal CVD. The catalyst used is sputter deposited Fe and the gaseous carbon source is ethylene. The growth temperature and time is 875 o C and 3 minutes respectively to produce a dense forest of vertically aligned MWCNT of an average length of ~50μm as shown in

Experimental

In order to determine the performance of the surfaces under repeated switching actions, an apparatus has been designed, in which a PZT actuator is used to support the planar coated surfaces as shown in Fig 4. This surface makes electrical contact with the hemispherical Au-coated probe to mimic the actuation of a MEMS relay microcontact. The apparatus has been designed to allow control of the gap and to allow the performance of the contact materials to be investigated ultimately over large numbers of switching cycles (>10 6 ). There are several methods to control the applied force as follows; 1) By controlling the gap [START_REF] Young | Roark's: Formulas for Stress & Strain[END_REF]. This can be achieved by turning the adjustment screw as shown in Fig 4 and the contact gap is monitored using a triangular laser, 2) By controlling the length of the actuator [START_REF] Duval | Characterisation of PZT thin film micro-actuators using a silicon micro-force sensor[END_REF], and 3) By controlling the amplitude of the supply voltage to the actuator. In the experiment presented here all other parameters are held constant, with the contact gap used to set the contact force at 1mN.

The contact resistance, R c is measured using the 4 wiremeasurement methods as shown in Fig 5 and6. The DC current source across the planar coated surfaces and microcontact is set at 1mA using a Keithley 580 microohmmeter. The number of cycles and contact resistance can be controlled and extracted by using the control and data acquisition program. The apparatus is enclosed and held at ambient air and room temperature. In this experiment, the PZT actuator is actuated up to 1000 cycles at 0.2 Hz under dry circuit conditions (maximum supply of 20mV at 1mA) with the contact resistance R c measured simultaneously. The aim of this initial study is to determine the stability of the contact surfaces, prior to longer duration testing at higher frequencies, an applied force of 1mN is used for consistency with previous results using a nano-indenter, [START_REF] Yunus | The Relationship between Contact Resistance and Contact Force on Au coated Carbon Nanotubes surfaces[END_REF]. The coated planar surface and Au ball are brought into contact at 0.2Hz using an applied square wave form, and the gap and amplitude adjusted so that a maximum load of 1 mN is reached. The targeted load is applied for ~3 seconds so that a representative average contact resistance value can be determined. The adhesive force increases with the number of cycles and is consistent with creep being one of the underlying physical mechanisms for the increase in adhesion [START_REF] Gregori | The interrelation between adhesion, contact creep, and roughness on the life of gold contacts in radio-frequency microswitches[END_REF]. The creep of the gold was shown in [START_REF] Yunus | The Relationship between Contact Resistance and Contact Force on Au coated Carbon Nanotubes surfaces[END_REF] The stable contact resistance data between 1-400 cycles in Fig 8 , shows the Au-Au interface is ~0.2Ω, while the Au-Au/MWCNT interface is ~0.5Ω. If we assume the standard Holm electrical contact model ( 1) and ( 2), then it is apparent that the main difficulty in comparing the two surfaces is in the determination of the conductivity. On first inspection if we assume the conductivity is the same in both cases then the contact area in the Au-Au/MWCNT interface would be smaller, this is assumed to not the case. Firstly the conductivity of the Au-Au/MWCNT interface is expected to be a function of the CNT surface structure and the Au surface; this has yet to be defined. Secondly it has It is anticipated that this can be improved in subsequent experiments by better process control. The contact resistance is much more stable than for the Au-Au pair over the 1000 loading cycles. This is believed to be due to the Au/MWCNT surfaces conforming to the shape of the Au hemispherical probe.

The dynamic impact on the Au hemispherical probe is absorbed by the Au/MWCNT surfaces thus reducing the wear. The sponge-like effect on Au-Au/MWCNT helps to reduce the deterioration. Furthermore, as the applied load is increased, more deflection occurs of the MWNTs closing the air gaps between the vertically aligned MWNTs thus improving the transfer of electrons [START_REF] Yunus | The Relationship between Contact Resistance and Contact Force on Au coated Carbon Nanotubes surfaces[END_REF].

Fig 11 shows a graph of load against displacement using a modified nanoindentation apparatus with Au-Au, and Au-Au/MWCNT contact pair. It shows the depth of penetration during the impact. The curve for Au-Au/MWCNT pair shows that there is much depth penetration compared with Au-Au pair (~70 nm and ~2500nm respectively). Once the indentation load is removed permanent displacement can be observed (~1400 nm). In [START_REF] Yunus | The Relationship between Contact Resistance and Contact Force on Au coated Carbon Nanotubes surfaces[END_REF] the results show an SEM image of the Au hemispherical probe contact surface after the load cycles having some damage to the Au surfaces where many small impressions on the Au hemispherical probe are detected. These impressions are due to the asperities on the MWNT surfaces. Moreover when the surface roughness (R a ) is measured in this region it has changed from ~400 nm to ~1.5μm.

Conclusion

The applied cyclic load and contact resistance between Au-Au/MWCNT composite contact pairs was investigated using a PZT actuator apparatus and R c measurement methods. This contact pair combination was compared with an Au-Au contact pair. Over 1000 load cycles the Au-Au/MWCNT contact pair demonstrated a much more stable contact resistance than Au-Au contact pair. This improvement is believed to be due to Au/MWCNT surface conforming readily with the dynamic impact of the Au hemispherical probe thus decreasing the tendency of smoothing and adhesion that damages the surfaces.

Fig 1 .

 1 Au is then sputtered on the upper surface of the MWCNT forest to produce Au/MWCNT composite coatings as shown in Fig 2. It is shown in Fig 3, that the Au penetrates the MWCNT surface to a depth of ~4 μm.

Fig. 1 .Fig. 2 .

 12 Fig. 1. Dense forest of MWCNT with average length ~50µm.

Fig. 3 .

 3 Fig. 3. Au penetration on MWCNT by sputtering. .

Fig. 4 .

 4 Fig. 4. Schematic side view of the test rig. A signal generator with voltage amplification is used to actuate the PZT actuator as shown in Fig 5. The PZT actuator's layers consist of Nickel (1 st layer), PZT material (Lead Zirconate Titanate) (2 nd layer), Nickel (3 rd layer) and Kovar (Nickel-Cobalt ferrous alloy, final layer).The resonance frequency of the PZT actuator is ~900Hz (1 st harmonic). In this experiment the PZT actuator is actuated at low frequency 0.2Hz to allow a quasi-static study of the contact surfaces. The dynamic force is measured using a piezoelectric force sensor[START_REF] Beckwith | Mechanical Measurements[END_REF][START_REF] Usher | Sensors and Transducers[END_REF][START_REF] Duval | Characterisation of PZT thin film micro-actuators using a silicon micro-force sensor[END_REF][START_REF] Dong | Fabrication and Characterization of microcantilever integrated with PZT thin film sensor and actuator[END_REF] situated as shown in Figs4 and 5. The force sensor is amplified using a charge amplifier and the dynamic force monitored.

Fig. 5 .

 5 Fig. 5. Schematic top view of the test system.

Fig. 6 .

 6 Fig. 6. Schematic of contact zone with its electrode and R c measurement.

Fig. 7 .Fig. 8 .

 78 Fig. 7. Example of load cycles (0.2 Hz) for an Au-Au contact pair at 1mN.The performance of the Au-Au/MWCNT surfaces is compared to a reference Au-Au contact pair under the same experimental conditions in order to assess their mechanical and electrical stability. A TaiCaan Technologies XYRIS 4000CL laser scanner is used to confirm any changes on the contact surfaces samples such as degradation and wear.4 Results and discussion

Fig 8

 8 Fig 8 shows the contact resistance of Au-Au and Au-Au/MWCNT pairs over 1000 load cycles at a maximum (quasi static) applied load of 1mN. The contact resistance of the Au-Au pair is initially ~0.2Ω and increases rapidly to 4-6Ω at 450 cycles. Under dry circuit conditions the contacts are unlikely to degrade by "hot-switching", therefore the increase in contact resistance is solely due to the mechanical deterioration of the Au-Au contact pair surfaces, reflecting the recognized problems of using soft metals for electrical contacts on a hard substrate. The reason for the sharp increase in R c of Au-Au pair at ~430 cycles is believed to be due to the initial smoothing of the Au surfaces which leads to increased adhesion[START_REF] Patton | Fundamental studies of Au contacts in MEMS RF switches[END_REF]. The smoothing is the result of the repeated impacts and timedependent deformation of the Au. Fig 9 which shows the damaged Au surface planar for the Au-Au contact pair.

Fig. 9 .

 9 Fig. 9. Scanned image of Au planar surface 201x201(0.2mmx0.2mm) using TaiCaan (Xyris 4000CL).

  during a single load cycle, as shown in Fig 10. Fig 10 shows the graph of load against displacement for an Au-Au contact pair. The experiment was carried out by replacing the diamond tip indenter with the Au hemispherical probe of a nanoindentation apparatus. The curve shows there is creep, a deformation that occurs over a period of time when a material is subjected to constant stress, even at room temperature. The force cycle exhibited in Fig 11 occurs over a longer holding time scale than that used in the test procedure.

Fig. 10 .

 10 Fig. 10. Graph of load against displacement for Au-Au contact pair. Fig 8 also shows contact resistance of Au-Au/MWCNT contact pair. The initial contact resistance (~0.7Ω) is higher for the Au-Au/MWNT pair. The likely cause is the difference of surface roughness between Au and Au/MWCNT coated planar surface and the irregularity of the Au film on the MWCNT.It is anticipated that this can be improved in subsequent experiments by better process control. The contact resistance is much more stable than for the Au-Au pair over the 1000 loading cycles. This is believed to be due to the Au/MWCNT surfaces conforming to the shape of the Au hemispherical probe.The dynamic impact on the Au hemispherical probe is absorbed by the Au/MWCNT surfaces thus reducing the wear. The sponge-like effect on Au-Au/MWCNT helps to reduce the deterioration. Furthermore, as the applied load is increased, more deflection occurs of the MWNTs closing the air gaps between the vertically aligned MWNTs thus improving the transfer of electrons[START_REF] Yunus | The Relationship between Contact Resistance and Contact Force on Au coated Carbon Nanotubes surfaces[END_REF].

Fig. 11 .

 11 Fig. 11. Graph of load against displacement for an Au-Au, and Au-Au/MWCNT contact pair.

  creep

Fig. 12 .

 12 Fig. 12. Scanned image of Au ball for Au-Au/MWCNTwith the sphere removed, contact pair 301x301 (0.4mmx0.4mm) using TaiCaan (Xyris 4000CL).

Acknowledgments

The authors thank Dr. David Smith of the School of Physics and Astronomy, for providing the facilities for developing the MWCNT deposition, and to Mr. Tim Hartley for his dedication in designing and fabricating the test apparatus.


Jean-Pierre Le Solleu
email: jean.pierre.lesolleu@delphi.com

Sliding contacts on liding contacts on liding contacts on liding contacts

Keywords:

Automotive suppliers use since decades Printed Circuit Boards (PCB) gold plating pads, as direct contact interface for low current sliding contacts. Several Gold plating processes are available on the market, providing various wear behaviour. Some specific galvanic hard gold 1 plating was developed on PCB's. This specific plating generates extra costs due to the material quantity and also the process complexity. In a cost driven industry, the challenge is to use a standard low cost PCB for systems requesting high reliability performances. After a brief overview of standard PCB manufacturing processes and especially Gold plating processes, the global experimental results of wear behaviour of three different gold plating technologies will be exposed and an explanation of the correlation between surface key parameters and wear out will be provided.

Introduction

When using PCB gold pads as static contact interface for sliding contact applications, we observed significant differences on wear behavior depending mainly on the type of Nickel / Gold plating used on the PCB. Three major technologies of Gold contact surfaces on PCB are mainly used and will be considered in this study.

• Galvanic Hard Gold electroplating • Electroless Nickel Immersion Gold (ENIG)

• Electrolytic pattern flash gold Hard Gold plating is a reference in term of performance and contact reliability for low current applications, but it is also the most expensive technology. Flash Gold technologies presents a real cost interest. As wear is the key driver for reliability of sliding contacts, the major focus of this study is given on the wear behaviour of different PCB technologies, in order to be able to quantify the contact performances during lifetime. Based on lifetime tests results, we could observe some significant wear differences between the three above mentioned gold plating technologies, depending mainly on the type of stationary contact surface.

The results presented in this paper are based on tests and analysis conducted on ENIG, Electrolytic flash Gold and galvanic hard gold printed circuit boards using the same contact slider for each test. A short overview of a typical wear failure with a 2µm Hard Gold application will be presented. The contact sliders used in this study (See Fig. 1) are standard bronze based contact spring, which are electroplated with a Nickel underlayer and a Gold Cobalt layer. The contact geometry is spherical with a radius at 0.9 mm. The contact force is set up at 0.35 N.

Usual gold plating types on PCB

Galvanic Hard Gold

Hard Gold is used where either a very resilient surface finish is required, or in the case of sliding applications or edge connectors, where a wear resistant and oxide free finish is required.

Unlike electroless finishes being an electrolytic process an electric current is required to plate the gold onto the board. The thickness of the gold coating can be easily controlled by the plating current (density) and plating time. In the days of old, edge connectors were regularly specified as requiring 7.5 microns of gold plating, our sliding applications normally plates 2 microns. To plate a sliding pad, a panel is normally masked with tape of peelable resist, and then dipped into the plating solution.

As the pads to be plated needs to be electrically connected to the same potential or electrode, special connection feeders are necessary. Those feeders have to be removed by etching or mechanical cutting when possible.

Flash gold

The flash gold PCB is designed to provide an oxidization / corrosion protection of the pads to ensure a safe soldering of the electronic components. It is initially not designed as a contact interface.

Due to the very low thickness of gold (25 to 100 nm), Gold flash is not sufficient to provide long term reliable contact resistance without additional protection. Any flash is porous, and exhibits the underneath Nickel layer through the pores, this generate an oxide and increase the contact resistance. To avoid corrosion or oxidization of the Nickel, a contact grease with specific protection properties (perfluor polyester base) is used. Two standard processes are used to obtain a gold flash; Electroless Nickel Immersion Gold (ENIG) and electrolytic pattern plating.

Electroless Nickel Immersion Gold (ENIG)

The electroless nickel is an auto-catalytic process depositing nickel on the palladium catalyzed copper surface. The reducing agent containing nickel ions must be replenished in order to provide proper concentration, temperature and pH levels necessary for this step in the ENIG process in order to create a consistent coating. The nickel is then processes with the gold, or a better description would be that the gold applies it-self to the nickel plated areas to protect the nickel until the soldering process. The gold thickness needs to meet tolerances to ensure that the nickel maintains its solderability.

Electrolytic Pattern Plating

A negative image of the pattern is first formed on the surface of the copper, using an appropriate photoresist. Gold is then electroplated to the required thickness all across the exposed areas of the pattern. The photoresist is stripped off in the next step, and finally the background copper etched off to define the circuit, using the plated gold as an etch resist. Though copper etchants do not attack gold, there is enhanced reaction in the vicinity of the gold-copper interface as a result of electrochemical potential between the two elements. This causes severe undercutting of the edges, and an undesirable gold foil overhang is formed as shown in Fig. 2. During subsequent cleaning and other handling of the circuit, this overhang could fold down the edges or sometimes fall off as small slivers. There is no effective way to remove the unwanted gold completely, and that has an obvious influence on the edge resolution of the finished circuit. Special chemistry and etching methods are under investigation to minimize these effects. By careful control it is currently possible to limit the gold overhang to about 0.5 mil 2 per edge.

Figure 2 Nickel & Gold overhang on electrolytic pattern plating

By comparing the wear of the blade crossing the edge and the blade on a continuous pad, no significant impact on wear could be demonstrated. The overhang is controlled and measured by the etch factor [START_REF] Holm | ELECTRIC CONTACTS[END_REF] .

Major risk is copper oxidization and electro migration as the copper edge is not protected, grease will provide an additional protection against electro migration

Key parameters driving wear

On hard gold contact pads

With a 2µm thick hard gold (AuNi or AuCo) layer on the contact pad the hardness values of both sliding partners are in the same range and wear is quite balanced between static contact surface and movable contact. Variations are mainly driven by process variations.

When the gold thickness is sufficient, the roughness has less influence, even hard gold will run in with the first pass of the blade. The influence of the gold thickness on wear was not quantified during this study and raises the question; at which minimum gold thickness will the Nickel roughness becomes the preponderant factor on blade wear? [START_REF] Féchant | Le contact éléctrique, l'appareillage de connexion[END_REF] 1 mil = 1 milli-inch = 25,4 µm 3 Etch factor is defined in standard IPC A-600 §

Another key factor to consider for the hard gold layer on PCB is the metallic deposit homogeneity.

A Printed Circuit Board sample exhibiting accelerated wear, on which hardness, thickness and roughness of gold were conform to specified values, was analyzed by generating a scratch with a nano indenter on the Nickel / Gold layer. The sanning electron microscope picture of the generated scratch (Fig. 3) shows: A Scanning Electron Microscope Edx material analysis inside the generated furrow in the gold layer could show that the black dots composition is mainly organic. Some deeper investigations of the gold deposit process and especially the analysis of the gold bath chemicals allowed us to link those black dots to the organic contamination of the gold bath. This example shows the particular sensitivity of PCB towards organic contamination. During the Nickel and gold plating process steps the whole laminate including photoresist films and polymers are immersed in the electrolyte, due to the nature of those components, it is easy to understand that if the electrolyte carbon filtration is not efficient, such organic contamination can occur and generate mechanical wear issues.

•

On flash gold contact pads

Grease

In our case the grease is chosen in order to provide a good oxidization protection and allow the contact functionality at temperatures down to -40°C. This protection is validated with specific thermal & humidity cycling, acid aqueous solution aspersion, and 4 Gaz corrosion test [START_REF] Antler | proceedings of the 18th Holm seminar on Electric Contact Phenomena[END_REF] . Detailed results are not presented in this paper; we will provide some global observations and additional questioning.

Based on lifetime tests and wear observations on the sliding blade, we could find out that depending on the PCB surface roughness, the mixture of grease and hard metallic wear debris could in some case accelerate the wear. When using grease in a sliding contact, the roughness of the hardest partner has to be maintained bellow a certain value and kept under control. This value is determined experimentally with abrasion measurements during lifetime tests. In best case we observed an abrasion improvement due to the grease from nearly 10%. The grease can also provides negative effects by increasing the contact bouncing time and the minimum contact force due to an increased film resistance. The grease is an insulating layer in the contact interface, with a certain viscosity (base oil) and flow pressure. It has been demonstrated that grease always increases the minimum contact force that is needed to establish a stable contact. The necessary pressure to press down the film present in the contact interface and provide the constriction resistance only, is higher on a lubricated contact compared to a dry, non corroded contact. Electrical contact bounce occurs in most switching contacts. In the general case, when two objects collide, there is inevitably a mechanical rebound. In the case of electrical contacts each bounce becomes a very fast make and break operation, what we call a "contact bouncing". As the grease has a certain viscosity, it influences the dynamic switching phase by increasing [START_REF] Antler | proceedings of the 18th Holm seminar on Electric Contact Phenomena[END_REF] The presence of non conductive particles (especially with PTFE based greases) is also a potential risk for the contact instability that is under investigation. The effect of grease on the contact resistance was not measured in this study as it was considered as "acceptable" by the switched system, even with a significant increase.

Hardness

On flash gold, due to its extreme thinness (around 12 nm), the gold layer mechanical properties are neglected, even if the gold layer can influence thermal or chemical effects. Hardness of the different Nickel layer was measured with a nano indenter XP from MTS using a Berkovitch tetraedric indent at 115,12°. Both electroless (NiP) and electrolytic Nickel have a hardness value above 500 Vickers, which is much harder than the standard Hard Gold plating used on the contact blades. Due to this big difference in hardness between stationary surface and sliding contact, the roughness of the hardest partner (in our case the PCB) becomes a preponderant parameter for wear behavior.

Roughness

Traditional roughness parameters as Ra and Rq are seen to be concerned only with relative departures from the mean line in the vertical direction; they do not provide any information about the shape, slopes and sizes of the asperities or about the frequencies of their occurrence. It is possible to have the same Ra and Rq values for surfaces of widely different materials and profiles. For example, on Fig. 5 are three surfaces that all have the same Ra, but you need no more than your eyes to know that they are quite different surfaces. In some applications they will perform very differently as well.

Figure 5 Example of surfaces providing same Ra value

To determine the "potential of wear" from our flash gold PCB surfaces we used the Abbott-Firestone curve (Fig. 6) to determine Rk, Rvk and Rpk and correlate those values with wear stage measurements on the sliding blade during lifetime tests. The roughness measurements were carried out with a STILL confocal microscope; equipped with a CHR 150 sensor with a depth of field of 300 µ m. It is a coaxial point sensor applying the principle of color coding of the area of measurement. The criterion for the wear stage that was used is the width of the wear trace on the sliding blade measured periodically during the lifetime. The correlation between wear and roughness parameters is shown in Table 1. The data were measured on two different types of PCB (ENIG and flash gold) and are the average taken out of 6 measurement points on each type of board.

Table 1 (measurement results of 3 roughness parameters)

On a PCB, the very thin metallic (Cu -Ni -Au) layers reflect the laminate waviness (provided by the glass fiber weaving) a filtering of the measurement data is necessary to extract the roughness parameters (Rk, RpK and Rvk). Fig. 7 shows an example of this filtering.

The first curve from top on Fig. 7 represents the raw data from measurement on the PCB Gold surface with the confocal microscope.

The second curve provides the waviness of the PCB laminate by filtering the data using a Gaussian filter with a cutoff length at 0,25 mm The third curve is the difference between the two previous ones in order to remove the waviness and take into consideration the micro roughness only and extract Rk, Rpk and Rvk parameters from the Abbott curve.

Nickel structure

The Nickel on Electroless Nickel Gold (ENIG) usually exhibits a columnar structure (Fig. 8) while electrodeposited Nickel grows in fine coats or strata (Fig. 9), providing a lower amount of wear debris and abrasion.

PCB surface preparation

To enhance the adhesion of liquid photoimageable soldermasks [START_REF] Kishimoto | proceedings of Holm Conference on Electrical Contacts[END_REF] and dielectric materials to copper surfaces of PCB a surface preparation (micro-etching) is necessary. Micro Etchants are used as pre-processor for all PCB manufacturing processes for the purpose of oxide removal from surface, removal of pollutants and foreign matters. This micro-etching step has a major influence on the copper roughness and by consequence on the final contact surface roughness too. Fig. 10 is providing an overview of copper surface after four different types of micro-etching; scrubbing, SPS type, Pumice brushing and organic CO-BRA BOND® SM.

The pictures show obvious differences in surface roughness for each type of micro-etching. However, it is not possible to directly link a microetching type to a given roughness as the processing parameters used for this micro-etching have also an influence on the final result on roughness.. A deeper investigation would be necessary to demonstrate the influence of each micro-etching type and process parameters on the roughness.

Conclusion

The results provided by the lifetime experiments, PCB surface and material analysis conducted in this study show that key physical characteristics on the product like hardness, roughness, brittleness are strongly dependent on process parameters like surface preparation (microeching), chemicals used for the layer deposit but also on the process type (electrolytic versus galvanic) in case of gold plating. Of course the key process parameters like time, current density are of major influence, but were not taken into account here because considered as under control.

Among the three types of PCB plating that has been studied, electrolytic pattern plating provides the most interesting properties in term of roughness. It is mainly linked to the fact that PCB surface preparation prior photoresist generates lower roughness in comparison to brushing used prior solder mask on ENIG process. In other words the process steps sequence strongly influence the final result. In addition, some shiny and wetting agents are added in the nickel bath, providing very smooth and shiny surface. Electrolytic Nickel layer usually grow as an addition of several horizontal layers (strata's), while ENIG plating provides a columnar growth of the Nickel layer.

• Hard Gold plating with a 2µm thickness is still the reference for sliding contact applications on PCB, nevertheless flash gold can be used as contact interface with some restrictions and great care about the surface topography when the switched electronic system allows some contact resistance variations up to a few Ohms (those variations were not quantified in detail here and are part of another study).

• PCB surface roughness is the key driver on wear behaviour for flash gold plating as the Nickel under layer is the preponderant factor. • As the gold is porous, usage of specific protective grease is necessary to prevent oxidization of the Nickel layer trough the pores (especially pitting corrosion). • The PCB must be chosen in order to ensure low abrasion; the selection can be done with Rpk, Rvk and Rk parameters. Preference is given to electrolytic Nickel and Gold deposits however this process needs some adjustments to avoid too high porosity. • Grease will improve wear only if the surface roughness of hardest contact surface is below a certain value, otherwise grease could even accelerate the wear out of the surface.

Figure 1

 1 Figure 1 Sliding contact schematic

Figure 3 Figure 4

 34 Figure 3 Scratch generated with nano indenter under controlled load During the displacement of the indenter generating the scratch, both tangential and longitudinal forces are recorded and displayed on the diagram shown in Fig. 4. When comparing two boards, the first one exhibiting accelerated wear (squared dots), the second one producing "normal" or acceptable wear (triangles), we can see on the plot of Fig 4 that the tangential force of the first board exhibits high discontinuity (erratic curve) whereas the tangential force of the second board follows a more continuous slope as normal force increases. Those discontinuities in tangential force on first sample reflect the non homogeneity of the layer and the formation of micro cracks and wear debris.

  the contact bouncing time which is the necessary time to stabilize the contact during the transient switching phase.

Figure 6

 6 Figure 6 Abbott -Firestone curve definitions

Figure 7

 7 Figure 7 Example of roughness data measurements and filtering

Figure 8 Figure 9

 89 Figure 8 ENIG surface overview

Figure 10

 10 Figure 10 Copper surfaces overview after micro-ecthing

Soldermask is a protective layer of acrylic-epoxy (normally green) applied over bare copper lines. Known as Solder Mask Over Bare Copper (SMOBC).


Gregorio Mentaberre
email: gregorio.mentaberres@uab.cat

Jorge Ramón López-Olvera

Encarnación Casas-Díaz

Laura Fernández-Sirera

Ignasi Marco

Santiago Lavín

J R López-Olvera

Effects of azaperone and haloperidol on the stress response of drive-net captured Iberian ibexes (Capra pyrenaica)

Keywords: Iberian ibex, Haloperidol, Azaperone, Drive-net capture, Acute stress

The physical capture of wild ungulates is performed for different purposes when anesthesia in field conditions is not possible or advisable. The use of tranquilizers may contribute to improved welfare of captured animals. This study aimed to evaluate the effect of azaperone and haloperidol on the stress response of Iberian ibex (Capra pyrenaica) through the evaluation of physiological, hematological, and serum biochemical parameters. Thirty-five Iberian ibexes were drive-net captured and randomly injected with azaperone (0.52± 0.07 mg/kg intramuscularly (IM); n=10), haloperidol (0.17± 0.04 mg/kg IM; n=10), or saline (0.5 mL IM; n=15) and physically restrained for 3 h. The variability of heart rate was lower in the azaperone-treated ibexes, suggesting a calming effect, and erythrocyte and biochemical parameters indicated vasodilation, splenic sequestration, hemodilution, improvement of renal perfusion, and a protective effect on muscle as a result of smooth muscle relaxation induced by azaperone. Haloperidol showed poorer results, maybe due to insufficient dosage. These results support the suitability of using azaperone in capture operations of Iberian ibex in order to reduce stress and prevent its adverse effects.

Introduction

The capture of Iberian ibex (Capra pyrenaica), an expanding although "near threatened" species (IUCN Caprinae Specialist Group 2007), is performed for translocation, population restocking, or scientific purposes. The resulting stress response is highly variable depending on the species and the capture method used [START_REF] Kock | Effects of capture on biological parameters in free-ranging bighorn sheep (Ovis canadensis)-evaluation of drop-net, drive-net, chemical immobilization and the net-gun[END_REF]. Drive nets have proved to be suitable for routine capture operations of Iberian ibex (Casas-Díaz et al. 2008a) and other species of wild ungulates [START_REF] Kenny | Successful field capture techniques for free-ranging Argali sheep (Ovis ammon) in Mongolia[END_REF][START_REF] López-Olvera | Effects of acepromazine on the stress response in Southern chamois (Rupicapra pyrenaica) captured by means of drive-nets[END_REF][START_REF] Montané | Effects of acepromazine on capture stress in roe deer (Capreolus capreolus)[END_REF]. Nevertheless, keeping stress to a minimum is necessary to improve animal welfare in terms of reducing anxiety and lessen mortality derived of the physiological negative effects of stress [START_REF] Spraker | Stress and capture myopathy[END_REF].

Catecholamines and corticosteroids released during the stress response, together with prolonged exertion, induce changes in hematological, serum biochemical, and physiological parameters [START_REF] Guyton | Textbook of medical physiology[END_REF]. Those parameters, or a combination of them, have been widely used as indicators of stress in wild ungulates [START_REF] Franzmann | Physiologic values in wild bighorn sheep (Ovis canadensis canadensis) at capture, after handling, and after captivity[END_REF][START_REF] Hattingh | Physiologicalresponse to manual restraint of wild Impala[END_REF][START_REF] Horalek | The heart rate of farmed red deer during and after transportation[END_REF][START_REF] Hyvärinen | Some effects of handling reindeer during gatherings on composition of their blood[END_REF][START_REF] Kock | Effects of capture on biological parameters in free-ranging bighorn sheep (Ovis canadensis)-evaluation of drop-net, drive-net, chemical immobilization and the net-gun[END_REF][START_REF] Marco | Effects of capture and transport on blood parameters in free-ranging mouflon (Ovis ammon)[END_REF][START_REF] Mautz | Blood-serum analyses of chemically and physically restrained white-tailed deer[END_REF][START_REF] Rehbinder | Influence of stress on some bloodconstituents in reindeer (Rangifer tarandus)[END_REF][START_REF] Waas | Real-time physiological responses of red deer to translocations[END_REF].

Animal welfare is improved when tranquilizers are used appropriately [START_REF] Ebedes | Use of tranquilizers in wild herbivores[END_REF]. The usefulness of acepromazine (ACP) to reduce stress in Iberian ibex has been demonstrated in previous studies (Casas-Díaz et al. 2008b). Haloperidol and azaperone (butyrophenones family) are short-acting neuroleptics which induce central dopaminergic and peripheral adrenergic blockade [START_REF] Booth | Psychotropic agents[END_REF][START_REF] Plumb | Veterinary drug handbook[END_REF]. Both have been described as effective sedatives in small-and medium-sized antelope and deer species (haloperidol: 0.06-0.45 mg/kg; azaperone: 0.05-2.83 mg/kg) [START_REF] Arnemo | Deer farming in Norway. A review of the currently available drugs that can be used for immobilization, pain relief and anaesthesia[END_REF][START_REF] Ebedes | Use of tranquilizers in wild herbivores[END_REF][START_REF] Read | Use of azaperone and zuclopenthixol acetate to facilitate translocation of white-tailed deer (Odocoileus virginianus)[END_REF][START_REF] Swan | The capture and care manual. Capture, care, accommodation and transporta-tion of wild African animals[END_REF].

In order to find other tranquilizers useful for the treatment of stress in the Iberian ibex, we evaluated the effect of azaperone and haloperidol on stress indicators of drive-net captured individuals.

Materials and methods

Thirty-five free-ranging Iberian ibexes (age range: 1-11 years; 4.1±2.51 years [mean±standard deviation]; sex: 11 males and 24 females), were captured with 10×10 cm mesh drive nets (Ziboni Ornitecnica, Bergamo, Italy), as described by [START_REF] López-Olvera | Comparative evaluation of effort, capture and handling effects of drive nets to capture roe deer (Capreolus capreolus), Southern chamois (Rupicapra pyrenaica) and Spanish ibex (Capra pyrenaica)[END_REF]. Capture operations (n=12; March 2005-November 2007) were performed at the National Game Reserve of Puertos de Tortosa y Beceite (40°50′ N, 0°30′ E), in Northwest Spain, and in the early morning, to avoid heat, and keep environmental conditions consistent.

Once trapped, ibexes were physically restrained, blindfolded, and held in a 4×4 cm mesh sack nets (Ziboni Ornitecnica, Bergamo, Italy) until released 3 h later. Blood samples were collected (disposable 10-mL syringes with 21-G×1 in needles) from the jugular vein at capture (time0) and each hour thereafter for 3 h (times1, 2, and 3). Two milliliters of each sample were placed in commercial tubes with anticoagulant (ethylenediaminetetraacetic acid-k 3 ) and the remainder was placed in tubes for serum collection, allowed to clot at room temperature, and centrifuged at 1,800 G. Blood samples were conserved and transported at 4°C until analysis, 2 to 5 h after collection. Serum was frozen at -20°C until analysis for a maximum period of 2 months. After collection of the first blood sample, random injections of azaperone-n =10; two males and eight females-(0.52±0.07 mg/kg [mean±standard deviation]) (Stressnil; Janssen-Esteve Laboratories, Barcelona, Spain), haloperidol-n = 10; 4 males and 6 females-(0.17 ± 0.04 mg/kg) (Haloperidol; Kern Pharma-Esteve Laboratories, Barcelona, Spain) or saline-n=15; five males and ten females-(0.5 mL) were administered intramuscularly (IM) in the hamstring muscle groups (semimembranous, semitendinous, and biceps femoris). Dosages intended for use were similar to those previously reported in other species of wild ungulates (0.2 mg/kg of haloperidol; 0.5-1 mg/kg of azaperone). Since doses were previously filled in syringes for standard weights of the species according to sex and age class, the resulting dosages were obtained dividing the injected dose by the real weight of each animal. Ibexes were kept in a quiet site close to the capture site until the end of the study (3 h altogether, from capture).

Ibexes were fitted with heart rate (Polar S710i; Polar Electro, Kempele, Finland) and body temperature (Mätman datalogger, Chipsobits Eltex AB, Almut, Sweden) recording devices, as previously described [START_REF] López-Olvera | Transport stress in Southern chamois (Rupicapra pyrenaica) and its modulation by acepromazine[END_REF], which is approximately 20-30 min after restraint and treatment administration. Both heart rate and rectal temperature were recorded at 60-s intervals until release and the mean values every 5-min calculated for statistical analysis. The erythrocyte and leukocyte counts, and the hemoglobin concentration, were determined by means of an automated laser analyzer (Advia 120,Bayer,Fernwald,Germany). The packed cell volume (PCV) was measured using a microhematocrit centrifuge (Hematospin 1400, Hawksley, Lancing, England) at 14,000 G for 6 min. The differential leukocyte count was performed by identifying 200 leukocytes on blood smears stained with a commercial Diff-Quick-like stain (Química Clínica Aplicada, Amposta, Spain). Biochemical parameters were determined by means of an automatic analyzer (Olympus AU400, Olympus, Tokyo, Japan), except for cortisol, which was analyzed with a commercial ELISA kit (EIA-1887, DRG Instruments, Marburg, Germany).

Repeated measures analysis of variance was used to detect significant differences by means of the PROC MIXED procedure of SAS System for Windows, V9.1 (SAS Institute, Cary, NC, USA). The main factor was treatment (azaperone, haloperidol, or saline), and the repeated factor was time. For each variable, sex, age, season, and interactions between these factors were considered in the model. When statistical differences between treatment groups at time 0 were obtained, values were expressed as a time 0 ratio. Estimated marginal means (command least-square means-LS MEANS-of SAS) were used due to the unbalanced distribution of animals between groups. In all cases, the minimum accepted significance level was P<0.05.

This study was approved by the Animal Welfare Committee of the Universitat Autònoma de Barcelona.

Results

Animals captured per operation ranged from zero to a maximum of eight animals (2.45 ± 2 [mean ± standard deviation]). Thirteen ibexes were captured in five capture events performed in spring and 22 in other seven capture events performed in autumn.

Both heart rate and rectal temperature decreased over time in all three groups (Fig. 1). However, stabilization of heart rate (i.e., lack of significant differences between two consecutive means) occurred earlier in the control ibexes (60 min after beginning of monitoring) than in the ibexes treated with haloperidol (70 min). Heart rate record did not stabilize in the azaperone group. The azaperone-treated ibexes displayed significantly higher values for this parameter than the controls at min 50, 70, and from 95 to 100. The haloperidol-treated ibexes also displayed higher values than the controls from min 40 to 50. On the other hand, individual and interindividual variability of heart rate was significantly lower in the azaperone-treated animals (11.81% ± 2.74% and 15.91% ± 5.44% [mean ± standard deviation]) than in the controls (15.57%± 4.11% and 17.82%±5.69%); in the haloperidol group (13.18%±5.68% and 17%±5.45%), these coefficients did not significantly differ from those in the other groups. No treatment differences in body temperature were observed between groups.

The erythrocyte count, PCV, hemoglobin, and total protein concentrations decreased over time in all groups, the stronger decrease being observed in the azaperonetreated ibexes, which also displayed lower values for these parameters than the control from time1 onward. The haloperidol group did not show treatment differences in these parameters when compared to the control and azaperone-treated groups (Fig. 2). A transient significant decrease of WBC count was observed in both the treated groups at times1 and 2.

Serum lactate and potassium concentrations decreased more in both the treated groups, serum creatinine concentration decreased only in the azaperone-treated animals, and serum urea concentration increased more in the control ibexes (Fig. 3). Serum activity of creatine kinase (CK) increased in both the control and the haloperidol groups, the stronger increase being observed in the untreated ibexes. The serum activity of alanine aminotransferase (ALT) increased only in the control ibexes. The azaperone group showed lower values of CK at the end of the study period and of ALT from time1 onward. The lactate dehydrogenase (LDH) and the aspartate aminotransferase (AST) increased in all the ibexes, the stronger rise being observed in the control ones (Fig. 4).

The remaining parameters (serum cortisol, glucose, cholesterol, bilirubin, chloride and sodium concentrations, and alkaline phosphatise activity) did not show clear treatment differences. Significant differences according to sex, age, and season or their interactions were not detected.

Discussion

Stress caused by capture and handling in wild ungulates can be assessed by measuring changes in hematological, biochemical, and clinical parameters [START_REF] Cross | Effect of physical restraint and xylazine sedation on hematological values in red deer (Cervus elaphus)[END_REF][START_REF] Kock | Effects of capture on biological parameters in free-ranging bighorn sheep (Ovis canadensis)-evaluation of drop-net, drive-net, chemical immobilization and the net-gun[END_REF][START_REF] Meyer | Hyperthermia in captured impala (Aepyceros melampus), a fright not flight response[END_REF][START_REF] Waas | Real-time physiological responses of red deer to translocations[END_REF][START_REF] Williams | Exertional myopathy (Capture myopathy)[END_REF]. According to [START_REF] Hopster | Validation of a heart-rate monitor for measuring stress-response in dairy-cows[END_REF], heart rate is a good indicator of the status of the autonomic nervous system when confronted with stressors. Both stress response and the effect of tranquilizers in the treated ibexes had already started when monitoring of heart rate began. The higher records observed in both the treated groups in our study could be due to the reflex tachycardia secondary to hypotension caused by the tranquilizers [START_REF] Plumb | Veterinary drug handbook[END_REF], as previously reported in tranquilized deer [START_REF] Diverio | Use of long-acting neuroleptics to reduce the stress response to management practices in red deer[END_REF][START_REF] Montané | Transport stress in roe deer (Capreolus capreolus). Effect of a short-acting antipsychotic[END_REF][START_REF] Montané | Effects of acepromazine on capture stress in roe deer (Capreolus capreolus)[END_REF]. Nevertheless, it increases at capture due not only to catecholamines, but also to physical activity and handling of the animal, so that other authors suggest that heart rate variability (HRV) may be a better indicator of stress. HRV is a measure of the state of the autonomic nervous system function (competitive activity of sympathetic and parasympathetic branches) of the individual and of its capacity to respond to environmental demands (Golberger 1991;[START_REF] Porges | Spontaneous oscillations in heart rate, potential index of stress[END_REF]. The lower HRV in the azaperone-treated ibexes suggests a calming effect, which is not observed in the haloperidol-treated group. Therefore, although a low degree of sedation is described for butyrophenones [START_REF] Plumb | Veterinary drug handbook[END_REF], the cardiovascular effects of azaperone could partially mask its beneficial ones. An inappropriately low dose could be the reason for this result in the haloperidol-treated ibexes. In our study, heart rate between the control and the azaperone-treated groups at each time; the dot indicates significant differences between the control and the haloperidol-treated groups; the asterisks indicate significant differences between both the treated groups. Different letters (a, b, c; p, q, r; x, y, z) indicate significant differences (P<0.05) between means within same treatment group along time stabilized before in the control group, which could also be attributable to the cardiovascular effects of butyrophenones [START_REF] Booth | Psychotropic agents[END_REF].

Body temperature is one of the main parameters to be considered when performing physical capture of wild animals, since its increase may determine the development of capture myopathy [START_REF] Spraker | Stress and capture myopathy[END_REF]. The increase cannot be explained by physical activity alone, but also by stressinduced hyperthermia (SIH; [START_REF] Bakken | Effects of environmental stressors on deep body temperature and activity levels in silver fox vixens (Vulpes vulpes)[END_REF]. Since SIH is an anticipatory response, tranquilizers can only modulate hyperthermia, not prevent it. Acepromazine modulated SIH in Iberian ibex subjected to the same capture and handling procedures (Casas-Díaz 2007). In our study, the lack of treatment differences in the temperature record is likely related to the lack of effect of butyrophenones over thermoregulation [START_REF] Plumb | Veterinary drug handbook[END_REF], as observed for haloperidol in blue wildebeest (Connochaetes taurinus) and goats (Capra hircus) undergoing different management or environment conditions [START_REF] Fick | The effect of bomahousing and long-acting tranquilizers on body temperature and food intake of blue wildebeest (Connochaetes taurinus)[END_REF][START_REF] Fick | Long-acting neuroleptics used in wildlife management do not impair thermoregulation or physical activity in goats (Capra hircus)[END_REF]. On the contrary, haloperidol succeeded to significantly decrease temperature in treated vs. untreated ibexes previously captured by the means of box traps (Casas-Díaz 2007). Since box-trap captured animals remain inactive for a few hours, the lack of physical activity could be the reason of this result. Nevertheless, some authors think capture-induced hyperthermia is caused predominantly by stress, more than by physical activity inherent to different capture methods [START_REF] Meyer | Hyperthermia in captured impala (Aepyceros melampus), a fright not flight response[END_REF].

Catecholamines released during stress response stimulate α-adrenergic receptors in the smooth muscle and cause splenic contraction and peripheral vasoconstriction [START_REF] Ganong | Sistema nervioso autónomo[END_REF]. The decrease of erythrocyte count, PCV, hemoglobin, and total protein concentration observed in all three groups indicates a return to baseline values after reaching its maximum at capture. However, the drop was found to be more significant in the azaperone-treated animals, probably due to vasodilation and splenic sequestration of erythrocytes owing to splenic capsule relaxation caused by azaperone [START_REF] Jain | Essentials of veterinary hematology[END_REF]. Hemodilution caused by the vasodilation could also explain the transient decrease observed in total protein concentration and in WBC count [START_REF] Plumb | Veterinary drug handbook[END_REF]. Haloperidol succeeded in significantly decreasing these parameters at higher doses in drive-net captured chamois (0.28± 0.12 mg/kg) and roe deer (0.3±0.04 mg/kg; Mentaberre et al. 1999a, b. Thus, the lack of treatment differences in these parameters in the haloperidol-treated ibexes vs. the controls could be due to insufficient dose (0.17±0.04 mg/kg). The leukogram followed the typical pattern of stress, with initial lymphocytic leukocytosis, and then corticosteroid-induced neutrophilia and lymphopenia [START_REF] Jain | Essentials of veterinary hematology[END_REF].

The lack of clear treatment differences in serum cortisol in our study indicates that it is not a good parameter to assess acute stress in Iberian ibex, as previously described in this (Casas-Díaz et al. 2008b) and other species of wild ungulates [START_REF] Ingram | Ultradian, circadian and seasonal rhythms in cortisol secretion and adrenal responsiveness to ACTH and yarding in unrestrained red deer (Cervus elaphus) stags[END_REF][START_REF] López-Olvera | Effects of acepromazine on the stress response in Southern chamois (Rupicapra pyrenaica) captured by means of drive-nets[END_REF][START_REF] Montané | Effects of acepromazine on capture stress in roe deer (Capreolus capreolus)[END_REF]. The great interindividual differences in stress response, stress-induced changes in costicosteroid concentrations, and other factors such as the circadian, ultracircadian, and seasonal patterns of secretion are the main reasons argued to reject serum cortisol as an acute stress indicator [START_REF] Guyton | Textbook of medical physiology[END_REF][START_REF] Rijnberg | Adrenocortical function[END_REF].

Muscular activity and catecholamine-induced renal vasospasm cause an increase of serum creatinine and urea concentrations [START_REF] Finco | Kidney function[END_REF][START_REF] Kaneko | Serum proteins and disproteinemias[END_REF]. Serum chloride, sodium, and potassium concentrations also increase due to decreased renal excretion and to release from working skeletal muscle (potassium; DiBartola and Autrain de Morais 2000; [START_REF] Gibert | Conséquences de la capture et des manipulations sur la physiologie des ongulés sauvages. Incidence pathologique Bilan et conaissances B Mens Off Nation Chasse[END_REF]). Higher values of serum lactate and lower values of serum total proteins, creatinine, and potassium concentrations have been reported in Spanish ibex in autumn (Casas-Díaz et al. 2008a). The higher percentage of ibexes captured in autumn in the azaperone group (eight out of ten) and in the haloperidol group (six out of ten) when compared to the controls (eight out of 15) in our study could explain the differences between groups found in these parameters at time 0. Since no differences among groups were observed in serum chloride and sodium trends, the lower values of serum urea and potassium concentrations in both treated groups and of serum creatinine concentration in the azaperone-treated group are more probably related to the vasodilatory effect of tranquilizers, mainly azaperone, at the muscular level, rather than to improved renal perfusion. Vasodilation prevents potassium leakage secondary to muscular damage, thus decreasing the risk of shock, ventricular fibrillation, and even death [START_REF] Guyton | Textbook of medical physiology[END_REF].

When muscles move, blood flow decreases as muscle contracts because of the contraction of the vessels and increases during relaxation, which is called the muscle pump [START_REF] Guyton | Textbook of medical physiology[END_REF]. The muscle pump is active when the animal is running but it is inactive when it is immobilized; thus, muscles of frightened and restrained animals are in a relatively isotonic state of contraction, which hinders blood flow into muscles. Serum CK, AST, LDH, and ALT activities, as well as serum lactate concentration, increase due to increased muscle-cell permeability, damage related to poor tissue perfusion, decreased heat dissipation, and hypoxia induced by catecholamines. These conditions may occur in capture-stressed wild ungulates and in those suffering from capture myopathy [START_REF] Vassart | Biochemical parameters following capture myopathy in one Arabian oryx (Oryx leucoryx)[END_REF]. Serum lactate concentration is a good predictor of muscular hypoxia and fatigue, main factors of the pathophysiology of capture myopathy [START_REF] Spraker | Stress and capture myopathy[END_REF], and CK and AST are the most sensitive, specific, and persistent indicators of muscular damage and, therefore, good predictors of capture myopathy too [START_REF] Williams | Exertional myopathy (Capture myopathy)[END_REF]. Muscular enzymes increased only (ALT) or more (CK, LDH, and AST) in the control group, which displayed significantly higher values of CK and ALT at the end of the study period. Serum lactate concentration decreased after capture in all three groups, probably indicating a return to baseline values, as previously reported for wild ungulates [START_REF] López-Olvera | Effects of acepromazine on the stress response in Southern chamois (Rupicapra pyrenaica) captured by means of drive-nets[END_REF][START_REF] Marco | Effects of capture and transport on blood parameters in free-ranging mouflon (Ovis ammon)[END_REF][START_REF] Montané | Effects of acepromazine on capture stress in roe deer (Capreolus capreolus)[END_REF]. However, lower values and stronger decrease were observed in both treated groups. These results indicate that both azaperone and haloperidol exert a protective effect against muscle damage, thus being useful to prevent capture myopathy. These two tranquilizers may yield this beneficial effect by blocking the α-adrenergic receptors or by stimulating the β 2 -adrenergic receptors and inducing vasodilation in striated muscle arterioles and, thus, increasing muscle blood flow, improving the oxygenation, and decreasing the anaerobic metabolism [START_REF] Booth | Psychotropic agents[END_REF][START_REF] Guyton | Textbook of medical physiology[END_REF].

In the present study, azaperone succeed to decrease erythrocyte parameters and creatinine whereas haloperidol did not, when compared to the control ibexes. However, similar effects were observed both for azaperone and haloperidol in muscular enzymes, lactate, urea, and potassium, the milder effects being observed in the haloperidol-treated animals. Since both tranquilizers belong to the butyrophenones family, similar action mechanisms are expected to take place. Thus, the more moderate action of haloperidol could be due to insufficient dose. It is likely that the beneficial effects of butyrophenones are mainly due to the induced peripheral vasodilation, which has a protective effect against the muscular damage that can occur during stress episodes in wild animals, and therefore, against the pathogenesis of capture myopathy.

The results obtained support the suitability of using azaperone in capture operations of Iberian ibex in order to reduce the stress response and prevent its adverse effects, mainly at the muscular level. More studies would be advisable to assess the effects of haloperidol at higher doses in the Iberian ibex. In addition to the use of tranquilizers, other measures to minimize stress should be employed such as blindfolding animals, maintaining a quiet handling environment, minimizing handling, and avoiding environmental conditions that promote hyperthermia.

Fig. 1

 1 Fig. 1 Mean heart rate (A) and rectal temperature (B) of the captured ibex. The arrows indicate stabilization of the control and the haloperidol-treated groups, respectively; the dots and triangles in the x axis indicate significant differences (P < 0.05) between the haloperidol-treated ibexes and the controls and between the azaperone-treated and the control ones, respectively

Fig. 3

 3 Fig. 3 Mean (A) serum lactate, (B) potassium, (C) creatinine, and (D) urea concentrations for the captured ibex. The triangles indicate significant differences (P < 0.05) between the control and the azaperone-treated groups at each time; the dots indicate significant differences between the control and the haloperidol-treated groups; the

Fig. 2

 2 Fig. 2 Mean (A) red blood cell (RBC) count, (B) packed cell volume (PCV), (C) hemoglobin, and (D) total protein concentrations of the captured ibex. The triangles indicate significant differences (P<0.05) between the control and the azaperone-treated groups at each time; the dot indicates significant differences between the control and the

Fig. 4

 4 Fig. 4 Mean (A) creatine kinase (CK), (B) aspartate aminotransferase (AST), (C) alanine aminotransferase (ALT), and (D) lactate dehydrogenase (LDH) for the captured ibex. The triangles indicate significant differences (P<0.05) between the control and the azaperone-treated

Acknowledgments We are grateful to the staff of the National Game Reserve of Tortosa i Beseit, especially to its former director, Mr. Jordi Romeva, and to the Cos d'Agents Rurals (Rangers brigade) of Catalonia for their invaluable collaboration in facilitating and capturing the animals. This research has been supported as research project CGL2004-00330/BOS of the Comisión Interministerial de Ciencia y Tecnología (CICYT). A native English-speaking instructor at the Universitat Autònoma de Barcelona provided editorial assistance. The experiments in this study comply with the current Spanish laws.


Maxime De

Marin De Montmarin

L10 -General < L1 -Market Structure, Firm Strategy, and Market Performance < L -Industrial Organization, L11 -Production, Pricing, and Market Structure|Size Distribution of Firms < L1 -Market Structure, Firm Strategy, and Market Performance

Keywords:

We investigate the two-stage competition in which two Internet Service Providers chosse sequentially their capacities and then their prices while facing a flow of new customers who decide to belong to one ISP or the other on the basis of a comparison of access prices and of expected congestion rates . At the equilibrium of the game a vertical differentiation between the Internet Service Providers endogenously emerges: the firm which provides the larger network has the lowest rate of congestion and the highest access price. The I.S.P providing the smallest network (thus the most congested) earns the larger profit. It will be noticed that the spontaneous functioning of oligopolistic competition produces a result similar to the Odlyzko's "Paris Metro

Pricing": at the equilibrium the two competitors propose different prices and rates of congestion, the most expensive one being also the least congested L12, L13

In this paper we investigate the static competition in prices and capacities between I.S.P which face a flow of new customers who decide to belong to one I.S.P or the other on the basis of a comparison of access prices and of congestion rates that they are supposed to anticipate in a rational way.

The interesting specificity of the approach presented here is that the level of quality of the service provided by an ISP depends not only on the capacity of its network (this is the common point with the model of Gabszewicz and Thisse) but also on the number of its customers which are connected, i.e. on the deman which is addressed to him/her. Since the latter, as we shall see below, is itself a function of the rate of congestion, there is a circular process which it will be necessary to analyze precisely

The main result result of this paper is the existence of two "miror" equilibria. In each equilibria the firm with the larger capacity sets the higher prices and is less congested than its competitor. Duopolistic equilibrium then reproduces the properties of the "Paris Metro Pricing" proposal of Odlyzko: consumer with different degrees of aversion to congestion are offered different (sub) networks: the more congestion adverse are allowed to pay more in order to benefit from a lower congestion rate.

The Model

There exist on the market two I.S.P each choosing a couple (price, quality), (p 1 , q 1 ) for firm 1 and (p 2 , q 2 ) for firm 2. The price is a lump sum which gives the right to the consumer to connect himself (hersel) to the network of the ISP during a given period of time. The quality q i of firm i's service is supposed equal to the ratio k i D i ( D i k i being the congestion rate of firm i's network) where K i represents the capacity of firm i's network and D i is the demand to firm i ( number of users).. This assumption is selected for the sake of simplicity. The basic idea is that the users always prefer a lower rate of congestion because the congestion present on a network represents a cost (measured in units of time) for the users since it delays or slows down the sending and the reception of data. This time increases with the number of connected users and decreases with the capacity of the network.

Consumers are characterized by their type θ wich measures their preference for quality (the higher is θ, the more important is the preference for quality). They subscribe to one of both firms. We make the simplifying assumption according to which θ is distributed uniformly on the interval [ 0,1 ]. The surplus of a type θ-consumer suscribing to firm i may be written as :

S i (θ) = u + θ q i -p i F o r P e e r R e v i e w
where u is a strictly positive parameter, the value of which is supposed very high so that at the equilibrium every user prefers to subscribe to one of the firms rather than staying out (i.e. the market is always covered).

T 1. We shall study the perfect sugame Nash equilibria, of the following three-stage game:

2. in a first stage the ISPs choose in a simultaneous way the capacity of their respective networks, the firm i investing an amount of money C(K i ) in order to reach a capacity K i . The function c is assumed increasing, convex and such that C(0) = 0. The capacity choices are irreversible and observable.

3. in a second stage, given the capacities previously selected, the ISPs choose, who rationally anticipate the equilibrium demand func- choose the low quality firm.

tions D i (p 1 , p 2 ), i = 1, 2,
θ * q 1 -p 1 = θ * q 2 -p 2 => θ * = p 2 -p 1 q 2-q 1 .
The demand addressed to the low quality firm firm is equal to θ * . The demand addressed to the high quality firm is equal to (1θ * ). Straightforwardly the demand addressed to each firm depends on the expected rate of congestion . The realized rate of congestion is itself a function of the demand. The assumption of rational anticipations imposes an equality between both expected and realized rates of congestion for each I.S.P.

Let us first consider the case where firm 2 is the high quality firm

(p 2 > p 1 ):
The demand addressed to firm 2 is thus :

D 2 = 1 - p 2 -p 1 q 2-q 1 ( 1
)
where In the same way for firm 1

q 2 = K 2 D 2 (2)
D 1 = p 2 -p 1 q 2-q 1 and q 1 = K 1 D 1
It follows that the difference between the "realized" qualities q 2-q 1 is a function of the difference between the expected qualities q a 2q a 1 :

q 2 -q 1 = K 2 (q a 2 -q a 1 ) (q a 2 -q a 1 ) (p 2 -p 1 ) - K (q a 2 -q a 1 ) (p 2 -p 1 ) (3)
Under rational expectations q a 2q a 1 = q 2q 1 and we determine the equilibrium value of q 2q 1 as a function of both access prices and networks capacities:

q 2 -q 1 = (p 2 -p 1 ) [K 2 + K 1 + p 2 -p 1 ] (p 2 -p 1) + K 1 (4)
In the symmetrical case where p 1 > p 2 one obtains obviously a symmetrical formula

q 1 -q 2 = (p 1 -p 2 ) [K 2 + K 1 + p 1 -p 2 ] (p 1 -p 2) + K 2 (5) When p 1 → p 2 , q 1 → q 2 .
This is the most interesting aspect of the model: a positive difference 6 in price generates a difference in quality so that the most expensive network is always the least.congested.. By replacing q 2q 1 by its equilibrium value one obtains the equilibrium demands for p 2 > p 1 :

D 2 = 1 - (K 1 + (p 2 -p 1) ) (K 1 + K 2 + (p 2 -p 1) ) (6)
D 1 = (K 1 + (p 2 -p 1) ) (K 1 + K 2 + (p 2 -p 1) )
When p 1 > p 2 the symmetrical formulas are:

D 1 = 1 - (K 2 + (p 1 -p 2 ) (K 1 + K 2 + (p 1 -p 2 ) (7) D 2 = (K 2 + (p 1 -p 2 ) (K 1 + K 2 + (p 1 -p 2 )
Finally when p 2 = p 1 we obtain

D i = K i K 1 +K 2 , i = 1, 2.
It is now possible to analyze the second stage equilibrium of the game.

There is at this level of the play a Nash equilibrium in price between the Internet Service Providers. When p 2 > p 1 ,the respective profits of both firms are:

π 2 = [1 - (K 1 + (p 2 -p 1 )) (K 1 + K 2 + (p 2 -p 1 )) ]p 2 -C(K 2 ) (8) π 1 = [ (K 1 + (p 2 -p 1) ) (K 1 + K 2 + (p 2 -p 1 )) ]p 1 -C(K 1 )
We obtains symmetrical formulas for p 1 > p 2 :

π 1 = [1 - (K 2 + (p 1 -p 2 ) (K 1 + K 2 + (p 1 -p 2 )) ]p 1 -C(K 1 ) (9)
π 2 = [ (K 2 + (p 1 -p 2 ) (K 1 + K 2 + (p 1 -p 2 )) ]p 2 -C(K 2 )
When p 2 = p 1 we obtain

π i = K i K 1 +K 2 p i -C(K i ).
For the sake of simplicity we shall now assume that C(K i ) = 0.5 * K 2 i .

Deriving π 2 with respect to p 2 one obtains

∂π 2 ∂p 2 = K 2 (K 1 + K 2 -p 1 ) (K 1 + K 2 -p 1 + p 2 ) 2 for p 2 > p 1 ( 10
)
∂π 2 ∂p 2 = K 2 2 + (p 2 -p 1 ) 2 + K 1 (p 1 -2p 2 ) + K 2 (K 1 -2p 2 + 2p 1 ) (K 1 + K 2 -p 2 + p 1 ) 2 for p 1 > p 2
Let us notice moreover that, for p 1 > p 2 we have

∂ 2 π 2 ∂p 2 2 = -2K 1 (K 1 +K 2 +p 1 ) (K 1 +K 2 -p 2 +p 1 ) 3 < 0.
Lemma 1:

1. The best reply correspondence of firm 2 is:

8 F o r P e e r R e v i e w (i) when K 1 ≥ K 2 : p 2 = +∞ for every p 1 ∈ [0, K 2 (1 + K 2 K 1 )] p 2 = K 1 + K 2 + p 1 - √ K 1 √ K 1 + K 2 + p 1 for every p 1 ≥ K 2 (1 + K 2 K 1 ) (ii) when K 2 ≥ K 1 : p 2 = +∞ for every p 1 ∈ [0, K 1 + K 2 ) p 2 ∈ [p 1 , +∞] for p 1 = K 1 + K 2 p 2 = p 1 for p 1 ∈ [K 1 + K 2 , K 2 (1 + K 2 K 1 )] p 2 = K 1 + K 2 + p 1 - √ K 1 √ K 1 + K 2 + p 1 for every p 1 ≥ K 2 (1 + K 2 K 1 ).
2. The best reply correspondence of firm 1 is as follows:

(i) when K 2 ≥ K 1 :

p 1 = +∞ for every p 2 ∈ [0, K 1 (1 + K 1 K 2 )] p 1 = K 1 + K 2 + p 2 - √ K 2 √ K 1 + K 2 + p 2 for every p 2 ≥ K 1 (1 + K 1 K 2 ) (ii) when K 1 ≥ K 2 : p 1 = +∞ for every p 2 ∈ [0, K 1 + K 2 ) p 1 ∈ [p 2 , +∞] for p 2 = K 1 + K 2 p 1 = p 2 for every p 2 ∈ [K 1 + K 2 , K 1 (1 + K 1 K 2 )] p 1 = K 1 + K 2 + p 2 - √ K 2 √ K 1 + K 2 + p 2 for every p 2 ≥ K 1 (1 + K 1 K 2 ).
Lemma 2: For any couple of networks capacities

(K 1 , K 2 ) ∈ < 2+
there exists a unique second-stage Nash equilibrium between the Internet Access Providers which is such that:

(i) if K 2 > K 1 then p 1 = K 1 +K 2 and p 2 = 1 2 ³ K 2 + p 5K 2 2 + 4K 1 K 2 (ii) if K 2 < K 1 then p 2 = K 1 +K 2 and p 1 = 1 2 ³ K 1 + p 5K 2 1 + 4K 1 K 2 (iii) if K 2 = K 1 then p 1 = p 2 = K 1 + K 2 . F o r P e e r R e v i e w
Taking into account Lemma 2, the profits of firm 2 are

π 2 = K 2 - 1 2 K 2 2 if K 2 ≥ K 1 (11)
π 2 = (K 1 + K 2 ) ( p K 1 (5K 1 + 4K 2 ) -K 1 ) K 1 + p K 1 (5K 1 + 4K 2 ) - 1 2 K 2 2 if K 2 ≤ K 1
and symmetrically for firm 1.

Lemma 3:

1. The reaction function of firm 2 is as follows:

(i) K 2 = 1 if K 1 ≤ K * where K * ' 0.829 (ii) K 2 = f (K 1 )
where f is a decreasing function such asf (0) = 1

(see Figure below 1 )
2. The reaction function of firm 1 is exactly symmetrical.

Proof: For a given K 1 there are two values of K 2 corresponding potentially to a local maximum of the profit π 2 :

K 2 = 1 et K 2 = f (K 1 ). K 2 =
1 can be a solution only for K 1 ≤ 1 In the same way

K 2 = f (K 1
) can be a solution only for f (K 1 ) ≤ K 1 , i.e. for K 1 lower than ' 0.666. Consequently for values of K 1 ranging between ' 0.666 and 1 it is necessary to compare the profits respectively associated to 1

The precise formula is too long and too complicated to be reproduced. The graph is plotted using Mathematica. It follows from the preceding Lemma that the reaction function of each firm is discontinuous, constant (capacity equalizes 1) between 0 and approximately 0.829 then decreasing after 0.829 where the best reply jumps down from 1 to approximately 0.649. We deduce easily now the equilibrium of the game.

Proposition 1 There are two perfect subgame equilibria of the model.

These equilibria are symmetrical and such that: Proof: See previous Lemmas.

K * 2 = 1, K * 1 ' 0.
There is thus at the equilibrium a vertical differentiation which is established in an endogenous way between the Internet Service Providers:

the firm which provides the larger network has the lowest rate of congestion and the highest access price ... It is interesting to notice that the corresponding equilibrium profits are 0.560435 for the I.S.P providing the smallest network (thus the most congested) and 0.5 for the I.S.P providing the largest network (thus the least congested). There is in the game studied here a first-mover' advantage: since there are two symmetrical equilibria each Provider prefers being the one which provides the smallest network and makes the highest profit.

  determined in the third stage, simultaneously choose their prices; 4. in the third stage each user chooses the network to which it will be connected given to the couple of prices (p 1 , p 2 ) chosen previously by the ISPs and to the couple of rates of congestion which she/he is assumed to rationally anticipate.1.2 The perfect subgame equilibriumAs usual the model is solved backward starting with the last stage, i.e. the determination of the demand functions. The type θ * -individual is indifferent between the two offers. All the consumers of types θ > θ * contract with the high quality firm while the consumers of types θ < θ *

Figure 1 :K 2

 12 Figure 1:

Figure 2

 2 Figure 2:

Editorial Office, Dept of Economics, Warwick University, Coventry CV4 7AL, UKSubmitted Manuscript