Colin Clive stars as Dr. Frankenstein; Frankenstein (1931) [SOURCE]

José Luis Giordano, Ph. D. (Physicist)

Associate Professor; University of Talca(Chile)

Engineering Sciences Department

Head; Materials Research Lab

 

PEER-REVIEWED PUBLICATIONS

Flux pinning in high-Tc superconductors under transport current cycles
J. L. Giordano and L. A. Angurel
Superconductor Science and Technology 14 (5) (2001)  655-658
Available upon request:  article.pdf (78 kB)

On reporting uncertainties of the straight-line regression parameters
J. L. Giordano
European Journal of Physics 20 (5) (1999)  343-349
Available upon request:  article.pdf (136 kB)

ABSTRACT: Due to the difficulties encountered in several aspects of experimental error estimation, undergraduate physics students usually use a list of "recipies" instead of taking a specific experimental errors course. Consequently, it is common to find university students who confuse basic concepts in the adjustment of experimental data. In this paper, the most conflicting point concerning linear regression are briefly reviewed. Confidence bands and a discussion about the use of a line through the origin are also included (*). In addition, the simplest expressions for expressing parameters to the appropriate significant figures from built-in calculator programs are also provided.

(*) This paper was originally submitted in October 1998 to the The Physics Teacher as a comment on "True Lines", an incorrect article by A. Mersereau and J. Metz (TPT 36 (1998) 174). The error was not recognized by the journal Editor, Dr. Clifford E. Swartz, who did not accept the comment for publication.

Optimal Control Model for the Critical State in Superconductors
Physical Review B 58 (14) (1 October1998-II) 9440-9449
A. Badía, C. López and J. L. Giordano
Available upon request:

ABSTRACT: Grounded on a variational principle, we present a generalization of the standard critical-state approach in type-II superconductors.  The free energy is minimized with the constraint |J(r)| < Jc for the macroscopic current density, posing the problem in the framework of the optimal control theory.  The application of this mathematical tool allows us to determine the critical state in which the system organizes itself.  This permits to confirm the critical-state hypothesis for an idealized one-dimensional geometry and to deal with multicomponent field situations, for which additional constitutive laws are provided.  A geometrical picture of the field penetration process has been developed and we obtain both analytical and numerical solutions for two-dimensional problems under an applied parallel field and superimposed transport current.

Calculation of the effective magnetic field under high voltage power lines
European Journal of Physics19 (4) (1998)  331-336
J. L. Giordano
Available upon request:  article.pdf (172 kB)

ABSTRACT: The calculation of the rms magnetic field due to several out-of-phase AC parallel currents involves some simple but instructive vector algebra.  In the present paper the expressions of the magnetic field under single-phase and three-phase lines are derived.  The analytical results are discussed and compared with measurements performed under a six-wire, high-voltage power line and near some electrical appliances.

Comment on
"Magnetic and electric field strengths of high voltage power lines and household appliances"
Physics Education33 (2) (1998) 84
J. L. Giordano
Available upon request:  comment.pdf (84 kB)

Due to the public controversy about the possible health effects of non-ionizing electromagnetic (EM) radiation on the human body, in a recent publication Austin [1] presented several direct measurements of magnetic and electric fields under high voltage power lines. To compare, the author also measured the EM fields generated by some home electrical appliances. The measurements were discussed in relation to the recommended maximum exposures given by the World Health Organisation, and finally, the author pointed out that people concerned about the health effects of EM fields generated by power lines should perhaps first consider daily used appliances. The article uses elemental common sense to deal on this old discussion, and it shows a logical step prior to deciding about Science matters. I would like to add some comments principally concerning the magnetic field.

(i) The possible effects of the EM fields generated by high voltage power lines has been a controversial topic in the media not only in relation to the potential hazard on health, but also on agriculture and cattle raising (mainly growth and milk production), which are very important matters in a global economy.

(ii) Much of the magnetic iron in the human blood is stored in the liver within a protein. The action of muscles and nerves involves electric currents which are basic for the operation of the human nervous system. Therefore, without any previous knowledge, terrible health effects from the magnetic field produced by most of the twentieth-century electric apparatus
could be presumed. However, many kinds of experiments with human volunteers, anesthetized dogs, mice, rats, pigeons, quail eggs, sea urchin eggs, flies and bacteria have been performed with no observed ill-effects and no subsequent evidence of injuries. The current understanding about magnetobiology is still limited. Meanwhile the health hazards within cigarettes and cars have been proved, but the danger of magnetic fields remains unconvincing.

(iii) It should be remembered that all known species (humans included) have evolved and live under a magnetic field of which its strength at present is about BE = 5x10⁴ nT (= 0.5 G). The established maximum level (10⁵ nT) for continuous exposure mentioned in [1] is two times BE. This means that following the guideline, humans could live safely under a total of 3 times BE, where "safely" only means that at present, there is not enough clear evidence or statistical correlation between the presence of weaker magnetic fields and health effects.

(iv) It could be very illustrative (at least for this subject) to normalize the magnetic data with BE. Using this gauge, the maximum value (80 nT) measured by Austin under a six-wire 220 kV power line is equivalent to 1.6x10^-3 times BE, and the field strength measured 0.3 m from away the microwave oven (7500 nT) is equivalent to 0.15 times BE. This means that these magnetic field strengths could be respectively 600 times and 6 times smaller than the typical local magnetic field strength.

Finally, I would like to add that the calculation of the magnetic field strength under a three-phase power line is not highlighted enough in electromagnetism textbooks, due to the fact that these books do not usually deal with measurements. These calculations involve some vector algebra. However, they are simple and very instructive. [2] In particular, the measurement reported in [1] fit well enough with the field generated by an in-phase double three-phase power line such as described by Austin, carrying a current amplitude of about 5.7 A each set. [3]

References

[1] Austin L 1997 Magnetic and electric field strengths of high voltage
power lines and household appliances Physics Education 32 (2) 108-110

[2] Giordano J L On the shielding and transport current distribution in
granular superconductors, and the application in the design of a
superconductor-based sensor magnetometer (In Spanish). Ph. D. Thesis,
University of Zaragoza. (1998)

[3] Giordano J L Calculation of the effective magnetic field under high
voltage power lines European Journal of Physics 19 (4) (1998)  331-336

Stroboscopic measurement of the power-line frequency using a bicycle
Physics Education32 (1997) 271-275
J. L. Giordano
Available upon request:  article.pdf (152 kB)

ABSTRACT: When certain rotating bodies are viewed in artificial light a stroboscopic effect can be observed that would not be seen in daylight. A simple analysis of this effect is presented here together with and experiment using a bicycle and a tachometer that allows students to determine the frequency of the mains electricity powering the light.

On the sensitivity, precision and resolution in DC Wheatstone bridges
European Journal of Physics18 (1997) 22-27
J. L. Giordano
Available upon request:  article.pdf (88 kB)

ABSTRACT: The voltage sensitivity and the measurement uncertainty due to the finite resolution in multi-decade and slide wire DC Wheatstone bridges have been reviewed and analysed in detail.  The use of the term 'precision' is discussed, and a criterion for maximum resolution with minimum power dissipation is shown.

Interaction between parallel magnetic fields and transport currents in YBCO superconductors
Physica C (North Holland)235-240 (1994) 2989-2990
J. L. Giordano, L. A. Angurel, F. Lera, C. Rillo and R. Navarro
Available upon request:

ABSTRACT: Magnetic AC susceptibility isotherms (80 K<T<83 K) have been measured on an YBa₂Cu₃O_7-x ceramic superconducting rod in longitudinal DC transport currents and magnetic fields.  The results are consistent with Critical State Theory predictions when transport and shielding currents are assumed in the same spatial region yielding lower field penetration and minimum magnetostatic energy.

A parallel-motion vibrating-sample harmonic magnetometer
Measurement Science and Technology 5 (1994) 509-513
J. L. Giordano and D. A. Esparza
Available upon request:  article.pdf (1 MB)

ABSTRACT: A new type of high-sensitivity vibrating-sample magnetometer (VSM) useful for measurements of soft and hard magnetic materials is described.  This instrument differs from the Foner type in the vibration system, which is a bar vibrating at its resonance frequency. Additionally, the electronic control preserves a constant vibration amplitude and versions with parallel and/or perpendicular motion can be designed.  Magnetic moments as small as 5 x 10^-8 A m² have been detected at room temperature and the overall accuracy is better than 0.5% using the simple prototype presented here.  An instrument with this system is easy to construct, relatively inexpensive and, due to its versatility, it could be a useful tool for research, industry and teaching purposes.
 
 

Medición estroboscópica de la frecuencia de la red eléctrica utilizando una bicicleta
(Spanish version of Phys. Ed. 32 (1997) 271-275 with Notes)
J. L. Giordano LumenVI (28) (1997) 30-37
Available upon request:

Acerca de la (in)existencia de la "fuerza centrífuga"
J. L. Giordano LumenVI (26) (1997) 31-37 (In Spanish)
Available upon request:  manuscript.pdf (226 kB)

High sensitivity magnetometer based on HTS ceramics
F. Lera, C. Rillo, J. L. Giordano, A. Martinez and L. A. Angurel
Superconductivity in Spain (1990-1992ResearchActivities) F. Yndurain (Ed.) 343-356
Madrid: MIDAS Program; 1993

Automatic 1,568 kJ capacitive-discharge 'C'-magnet yoke magnetizer-demagnetizer
for 1 T magnetization of 18" loudspeaker pole pieces in a 20 cm (8,000 cc) gap
Development and Construction Technical Manual; Giordano J L and Esparza D A; 1988
Internal Report; Centro Atómico Bariloche; Comisión Nacional de Energía Atómica; Argentina
 
 

On the shielding and transport current distribution in granular superconductors,
and the application in the design of a superconductor-based sensor magnetometer
(In Spanish)
J. L. Giordano Ph. D. Thesis (1998) Universidad de Zaragoza, Spain
Partially published in:
    Superconductor Science and Technology 14 (5) (2001)  655-658
    Physical Review B 58 (14) (1998) 9440-9449
    Physica C (North Holland)235-240 (1994) 2989-2990

ABSTRACT: Several configurations in magnetometry, current transport and magnetic field generation applications involving type-II superconductors lead to a
complex shielding and conduction current distribution. Normally, these situations cannot be solved by the application of the standard Critical
State Model which does not provide the necessary constitutive equations to know the current distribution in a two-component problem.

In this work, the problem of a transport current and applied field parallel to an infinite sample, was approached both theoretically and experimentally.
     In order to minimize the system energy, a distribution in which shielding and conduction coexist in the same peripherical region was found by using the optimal control theory. On the other hand, the shielding is cancelled from the center of the sample in order to keep the externally fixed conduction current in the full penetration regime.
     A simplified model is also proposed with the main characteristics of the minimum energy variational one. In the proposed model, hysteresis and field dependance with the local field on Jc were added. The model has been implemented with numerical methods avoiding the intrinsic complexity of variational approaches.

On the other hand, the problem was also experimentally studied carrying out inductive and resistive experiments performing simultaneous measurements on
relatively long YBCO samples.
     Comparing with other models and with the experimental results, the current distribution effect on the magnetic properties is better understood. Particularly, within the experimental conditions used, the distribution which best fits the measurements is the coexistence of shielding and conduction currents.

In the last part, the development of a nanotesla magnetometer with high-Tc superconducting sensor is presented. The phase-compensation network design is detailed by using a straightforward method which avoid time-consuming trial-and-error procedures in the feedback loop design. The superconducting ceramic sensor optimization by applying a bias current in the studied parallel configuration is discussed. Finally, some applications are presented.

CONCLUSIONS: (A) Conduction and shielding current distribution
In this work several experimental results with parallel fields and longitudinal currents simultaneously applied on YBCO samples are presented, such as resistive measurements Vd(I), susceptibility X1(HAC), X1(HDC), X1(IDC), X1(T), X2(HAC) and X2(IDC), and magnetization Mz(HDC) and Mz(IDC). These experiments show the effect of transport on the magnetic properties in the intergranular regime. The main distinctive characteristics are the following:
     (i) it was corroborated that the effect of transport commences to be distinguishable after a current value IDC of about 25 or 30 % of Ic0; moreover, this effect is more remarkable close to Ic0 instead of proportional to IDC.
     (ii) the dissipative regime appears when there is a considerable amount of shielding; for a given IDC and temperature T, the dissipative static field is between the penetration and the percolative critical field of the junctions, Hpen(IDC,T) < HD(IDC,T) < Hc2J(T).
     (iii) Qualitatively, the effect of transport is similar to the temperature one.
     (iv) the field induced by the conduction current is strongly pinned in the material limiting its shielding capability.
     (v) Depending on the material, mucer(T) can be affected by IDC even when the total surface field is under Hc1g(T).
     (vi) Within the experimental conditions applied, there are not noticeable intergranular effects when the different zero-field-cooling, field-cooling or current-cooling processes are used.

In order to have good mechanical resistance and low enough effective resistivity in the current contacts, a sintering process was studied and used. The process which allows the conduction of several ampere without noticeable dissipation is described.

The development of a probe designed to perform simultaneous resistive and
inductive measurements in high sensitivity susceptometers and SQUID
magnetometers is also described. Experiments up to IDC = 3.5 A were carried
out without any interference with the SQUID detection system.

In this work the characteristic magnitudes of the Critical State problem
with field and current simultaneously applied are shown. The dimensionless
formalism does not only give a clearer physical meaning, but also the
treatment with reduced magnitudes is more convenient for the analytical
calculations, numerical implementation and even when comparing to
observations. Particularly, it was shown that when scaling the experimental
susceptibility with the penetration field and the ceramic permeability of
the material, a general behaviour could be found for a given sample. This
behaviour was illustrated with the intergranular relative permeability
curve muJ(HAC/Hpen) for a given reduced current IDC/Ic*, where Ic* is
determined from inductive experiments.

In this work an approach to the Critical State problem with optimal control
theory is proposed. Particularly, the variational approach is used to solve
the two components problem with parallel current and field, obtaining a
complete algebraic and partial differential system of equations with two
kinds of boundaries (i.e., partial or full penetration cases).
     From the minimization of the energy, the variational approach gives
the criticality of the vortex dynamics (i.e., the Critical State equation),
and a second constitutive equation which determines the distribution of
conduction and shielding within a type-II superconductor. By using the
Bean-London dependance, Jc(B) = Jc0, the problem of an infinite slab and
cylinder was analytically and numerically solved, respectively.
     Within the distinguishable characteristics of the solution it should
be remarked that the field and currents penetrate in the slab (cylinder) in
a peripheral coexistence of conduction and shielding region where the
corresponding current densities are uniform (approximately uniform), and J
and B are perpendicular (approximately perpendicular) until full
penetration.
     The minimum energy solution predicts the observations (i), (ii) and
(iii), since the conduction current lines are "diluted" in the shielding
region. On the other hand, numerical results obtained in this work by using
other models with separate shielding and conduction regions contradict
these experimental facts.

A model where conduction and shielding coexist in a peripheric penetration
region and have the same Jc(B) local dependance was developed. This model
simplifies the treatment and allows the implementation of more general
dependances including hysteresis phenomena.
     The uniformity of the currents in the variational solution is loose
over the full penetration regime. However, the discrepancies of the
magnetic properties predicted by the variational model and the simplified
one could be neglected in most cases. Future extensions of the model should
be considered as relevant effects, such as shape factors, flux creep and
dispersion of the parameters which were neglected in this work.
 

CONCLUSIONS: (B) Magnetometer
A magnetometer based in the sensitivity to the weak magnetic field of YBCO
samples was designed and built operating at maximum sensitivity in liquid
nitrogen. The intrinsic sensor limitations such as its strong dependance of
the linear range, frequency response and the sensitivity to the sample
conditions, have been avoided with the design of a feedback electronic
system which keeps the sensor as a null detector.
     The sensitivity of the prototype is near 2 nT with a resolution of 1
nT (= 10 microgauss), capable of detecting variation of static and AC
fields (up to 1 kHz) 105 times smaller than the Earth local field with a
spatial resolution better than 1 cm.

An adjustable compensation series-in-opposition coil was designed in the
transducer system instead of the common twin coils, and an automatic system
for fine compensation is proposed.

The design procedure is described step by step by examining the basic
design criteria. Particularly, a straighforward method to design the
compensated error amplifier is detailed and adapted to the magnetometer
design.

The effect of a steady current in the sensor was experimentally shown and
the application of a current as a polarization method of the sensor was
discussed.

The magnetometer prototype has shown to be a useful instrument to measure
magnetic interference and to characterize ceramic samples. It is a simple
low cost and very sensitive susceptometer. However, its great disadvantage
in relation to the flux-gate types is the need to cool the sensor.

Finally, the developed prototype has an enormous educational value in the
high-Tc superconductivity and in the advanced instrumentation, since
concepts such as magnetic properties of granular superconductors, Critical
State, weak junction models, low noise electronic, negative feedback, null
detection method and spectrum signal analysis are involved.

Vibrating-sample harmonic-magnetometer
and preparation of Sm Co 1:5 intermetallic compounds
(In Spanish)
J. L. Giordano Master Sc. Thesis (1986) Universidad de Buenos Aires, Argentine
Partially published in :
    Measurement Science and Technology 5 (1994) 509-513

Transport Current Effects on Magnetization in High-Tc Superconductors
J. L. Giordano*(1) and L. A. Angurel(2)
(1) Engineering Sciences Department; Engineering Faculty
University of Talca; Camino a Los Niches km 1, Curicó, Chile
(2) Materials and Fluids Sc. and Tech. Dept.; Higher Politechnical Center
University of Zaragoza; María de Luna 3 - E-50015; Zaragoza, Spain

ABSTRACT: We present magnetization measurements when cycling conduction current are superimposed by a magnetic field within High Tc Superconducting YBaCuO cylinders. The effects of a varying conduction current on the shielding capacity of a pinned superconductor are studied in the framework of a generalized Critical State Model and the Flux-Line Cutting process. Additionally to a strong pinning which reduces the shielding capability of the superconductor, it was found that the magnetization decreases in each cycle for moderate current amplitude. On the other hand, when the current amplitude is relatively high, ’butterfly’ loops are observed. These preliminary results are very useful for the current distribution and the vortex dynamics understanding in hard superconductors.
 

Tracing I-V Curves of Electronic Components on Standard Oscilloscopes
J. L. Giordano*(1), M. T. Mozó E.(2) and A. A. Soto V.(2)
(1) Engineering Sciences Department
(2) Industrial Engineering Career
Engineering Faculty, University of Talca; Camino a Los Niches km 1, Curicó, Chile

ABSTRACT: When testing or designing with nonlinear discrete components in Physics, Electronics and Materials Sciences fields, knowledge of the current I flowing through an electronic device against the voltage V across it is required. Most commercial versions of curve tracers (which display at the same time a family of I(V) characteristic curves for different control currents) are expensive and limited to test diodes and transistors. However, a single I(V) curve for 2 terminal electronic component could be generated on a standard scope, with few common and inexpensive components. In this work, we present the simplest method and circuitry to generate an I(V) curve for 2-3-4-terminal devices on a standard two-channel scope, with few common and inexpensive components.
 

Modelización del problema de flotabilidad de alimento extruído para acuocultivos
J. L. Giordano*(1), A. Iriarte G.(1), I. Ruíz-Tagle(2), M. T. Mozó E.(3) y A. P. Ponce R.(3)
(1) Departamento de Ciencias de la Ingeniería
(2) Instituto de Química de Recursos Naturales
(3) Carrera de Ingeniería Civil Industrial
Facultad de Ingeniería, Universidad de Talca; Camino a Los Niches km 1, Curicó, Chile

ABSTRACT: El alimento extruído para peces y moluscos se fabrica como ’pellets’ de diferentes diámetros. En salmónidos, la alimentación es el 50% de su costo en el mercado. En ciertas condiciones de utilización, cerca del 10% del alimento se pierde por flotación (Para una empresa típica en el sur de Chile, representa pérdidas de unos 750 mil dólares por año). En este trabajo resumimos la modelización del problema desde el punto de vista energético, en el que hemos considerado aspectos físico-químicos estáticos y dinámicos, como resistencia del aire, movimiento de un sólido rígido, tensión superficial aire-sólido-agua, formación de ondas de gravedad, adherencia de microburbujas, chorro de Rayleigh, balance de fuerzas estáticas, solubilidad y resistencia laminar y turbulenta del agua.
 

* Posters presentation respectively in
Session 9.12: Condensed Matter; Superconductivity,
Session 10 - Applied Physics; Instruments
Session 16 - Others
88th Meeting of the Argentine Physics Association (AFA)
September 22-25, 2003; San Carlos de Bariloche, Argentina
Available upon request:

Inexpensive curve tracer circuit for electronic components characterization and testing
J.L. Giordano*, A. A. Soto V. and M. T. Mozó E.
* Poster presentation
XIII Chilean Symposium of Physics of the Chilean Physical Society (SoChiFi)
November 13-15, 2002; Concepción, Chile
Available upon request:  poster.MacIntosh (376 kB)

INTRODUCTION: Experiments involving Electronics are very popular in both high-school and undergraduate lab experiments and projects. When testing or designing with nonlinear discrete components, knowledge of the current I flowing through an electronic device against the voltage V across it is required. Most commercial versions of curve tracers (which display at the same time a family of I(V) characteristic curves for different control currents) are expensive and limited to test diodes and transistors.
IN THIS WORK we show the simplest method and circuitry (adapted from [1]) to generate a single I(V) curve for 2-3-4-terminal devices on a standard 2-channel scope, with few common and inexpensive components.

APPARATUS: An AC-voltage VS(t) is applied to the device under test (D.U.T.) through a sensing resistor R (Fig. 1). The inverted voltage across R (which is proportional to the current I) and the voltage V on the D.U.T. are simultaneously measured on the vertical VY (= ?IR) and horizontal VX (= V) DC-coupled inputs of a two channel oscilloscope working in the XY-MODE.
 Since VS is AC, the load line is parallelly oscillating, and the operating point is a moving spot on the screen, which generates a view of the IR(V) curve (Fig. 2). Another tap in the transformer is used as additional power supply for controlled devices (Figs. 7, 9, 11, and 13).

CONCLUSIONS: This method could be useful to develop experiments for Materials Science, Electronics and Electromagnetism university courses. Also, the circuit can be implemented by high-school students themselves to test and study components during their lab activities.

Flux pinning in high-Tc superconductors under transport current variations
J.L. Giordano* and L. A. Angurel
* Poster Presentation
International Workshop on Critical Currents(IWCC 2001)
June 4-7, 2001; Institut für Materialsphysik, Universität Göttingen; Göttingen, Deutschland
Available upon request:  poster.doc (106 kB) and poster.pdf (55 kB)

ABSTRACT: The pinning process within a hard superconductor in a two component configuration was experimentaly studied under a cycling a transport current. The axial component of the magnetic moment of polycrystalline YBaCuO cylinders was directly measured in a SQUID magnetometer under longitudinal currents and simultaneously applied stationary parallel magnetic fields.

The effect on the axial magnetization of the current cycling (i.e., the azimuthal field cycling), shows a strong pinning which reduces the shielding capability of the superconductor. Additionaly, two different behaviour were found for moderate current amplitud of the cycle (depending on the field penetration region at a given temperature and applied field strengh), the magnetization decreases in each cycle. On the other hand, when the current amplitud is relatively high "butterfly" loops are observed.

This evidence indicates that the cutting and cross-flow of nonparallel flux lines occurs in the weak links regime of high-Tc superconductors. The results can be analyzed in the framework of a generalized critical state model.

Theorems about the vertex of the parabola 
J.L. Giordano*

ABSTRACT: The graphic of  ƒ(x) =  ax2 + bx + c in the plane is a curve so-called parabola, which could be also defined by the coefficient a and the coordinates of the vertex V = (xv, yv).  It is well known that changes in the constant parameter c "move" the related parabola vertically.  This brief work shows that if one of the other two coefficients changes, the position of the vertex changes on specific curve.  This is an unknown or at least less divulged aspect which could be useful in the graphical interpretation of some Physics problems.

A phenomenological approach to leakage in magnetic circuits
J.L. Giordano*

ABSTRACT: In this work, a steady state flux leakage model for gapped ferromagnetic devices is proposed to understand the noticeable experimental discrepancies between an ideal magnetic circuit (MC) and a real device.  The model considers the best known leakage contributions, such as "limb" and "fringing" fluxes, and also the coil location and the effect of a stray "inverse" flux on the winding.  Despite the fact that this last effect could be an important factor in many practical situations, its effect is apparently not well divulged.  Preserving the simplicity of the standard one-dimensional MC analysis, an experimental straightforward procedure to estimate the three-dimensional leakage flux from direct measurements on a prototype is also shown.  Severe experimental discrepancies between this real apparatus and the ideal MC are shown and experimentally studied.  The prototype was built with a commercially available ferrite core.  The gap is variable and the winding is formed by a set of three coils separately wound. These coils are vertically placed with air gaps inside and lateral to the central coil, in order to study location effects for different gap lengths.
The method could be valuable for design and the apparatus could also be very instructive for introductory Physics courses.

Minimum energy model for the current distribution in hard superconductors
J.L. Giordano*, L.A. Angurel, A. Badía, C. López and F. Lera

ABSTRACT: The problem of a transport current and simultaneously applied field parallel to an infinite hard-superconducting sample, was approached both theoretically and experimentally.
By minimizing the system energy of an originally virgin sample in the framework of the Optimal Control Theory, a distribution in which shielding and conduction coexist in the same peripherical region was found.
Adding hypothesis about hysteresis and field dependence with the local field on the critical current density Jc, a simplified model (previously proposed) was justified.  This phenomenological model has been implemented with numerical techniques and the field profiles within the sample are found by shooting-methods.
The problem was also experimentally studied from 7 K to Tc carrying out inductive and resistive experiments (from 0 A to the dissipative regime) performing simultaneous measurements on relatively long YBCO samples. Scaling parameters are determined in order to reduce the observations and to compare with numerical results.
Comparing with the results from other models and from the observations, the current distribution effect on the magnetic properties was better understood.
Particularly, within the experimental conditions used, the current distribution which best fits the measurements is the coexistence of shielding and conduction currents.

* Posters presentation
XII Chilean Symposium of Physics of the Chilean Physical Society (SoChiFi)
November 22-24, 2000; University of Santiago; Santiago, Chile
Available upon request:

Modelling current distribution in granular superconductors:
transport, inductive and simultaneous measurements on YBCO samples
J.L. Giordano*, L.A. Angurel, F. Lera, A. Badía and C. López
* Poster presentation in the Flux pinning and ac losses; session (LP7)
4th European Conference on Applied Superconductivity (EUCAS'99)
September 14-17, 1999; Sitges, Barcelona; Spain

ABSTRACT: The interplay of electric transport and magnetic shielding currents within
a type-II superconducting wire is an interesting technological problem
deeply related to the current distribution capable of both tasks
simultaneously: to shield an external applied magnetic field carrying a
given transport current.

This problem has been experimentally studied on YBa2Cu3O7-x policrystalline
ceramic cylinders under longitudinal transport DC currents and parallel
magnetic fields at temperatures up to 0.9xTc, by using pulsed currents
under DC fields, and AC-susceptibility and magnetization techniques with
simultaneous transport measurements (from 0 to Ic).

A theoretical approach has been made in the framework of the Critical State
Model. The measurements were analyzed and compared with the predictions
obtained with a minimum magnetic energy model. In this current distribution
model low field penetration is obtained for a given transport current I,
and low sensitivity of the AC-susceptibility for currents up to Ic/4 takes
place in agreement with the experimental observations.

Modelling of shielding and transport current of granular superconductors:
transport, inductive and simultaneous measurements on YBCO cylinders
J. L. Giordano* , L. A. Angurel, F. Lera and A. Badía
* Contributed oral presentation
Science and Engineering of HTC Superconductivity Symposium
9th. International Conference on Modern Materials and Technologies
14-19 June 1998; Firenze, Italy

Generalizing the Critical State Model for Superconductors through Optimal Control
C. López*, A. Badía and J. L. Giordano
* Contributed lecture
Venice-2/Symposium on Applied and Industrial Mathematics
11-16 June 1998; Ateneo Veneto, Venice, Italy

Interaction between parallel magnetic fields and transport currents in YBCO superconductors
J. L. Giordano* , L. A. Angurel, F. Lera, C. Rillo and R. Navarro
* Poster presentation
International Conference on Materials & Mechanisms of Superconductivity and High-Temperature superconductors
5-9 July 1994; Grenoble, France

Transport current influence on the sensitivity of high-Tc superconductors ceramics to magnetic fields
J. L. Giordano*, L. A. Angurel, F. Lera and C. Rillo
* Poster presentation
3rd Conference of the European CeramicSociety
September 12-17, 1993; Madrid, Spain

High Tc Superconductor sensors for magnetic field detection
L. A. Angurel*, J. L. Giordano, A. Martinez, F. Lera, C. Rillo,R. Navarro and P. Tellez
* Contributed oral presentation
5th International Congresson Industrial Metrology (1992) Metromatica/91; CPSI; 13-15 November 1991; Zaragoza, Spain
Proc. 5th Intl. Congress on Ind. Metrology (1992) 405-414
 
 

SUPERCONDUCTIVIDAD APLICADA 
J. Ossandón, J. L. Giordano,  N. S. Cruz C., V. M. Conte  P. and V. Ibarra A.
Stand in the FERIA DE LA FÍSICA
12-16 October 2005; Museo Interactivo Mirador (MIM), Santiago, Chile
XI-Semana Nacional de la Ciencia y la Tecnología; CONICyT - Explora / PNBT

Thermoelectricity: Discovery, Foundations and Applications
J. L. Giordano
Invited Conference with Experimental Demostration
Second Meeting of Scientific Student of the Maule Region
4-5 July 2002; Instituto de Química y Recursos Naturales, University of Talca; Chile
and
San Fernando College (San Fernando; Chile); 12 July 2002

Electromagnetic Properties of Superconductors
J. L. Giordano
Invited Conference with Experimental Demostration
First Meeting of Scientific Student of the Maule Region
3-4 November 2000; Instituto de Química y Recursos Naturales, University of Talca; Chile

High-Temperature Superconducting Magnetic Sensors
J. L. Giordano
Theoretical and Experimental Lecture
High-School Upgrade Lecture for High-School teachers
18 December 1992; Faculty of Science, University of Zaragoza; Spain

Control and Digital Electronics Systems
J. L. Giordano
Theoretical and Experimental Workshop
Sixth Argentine Physics Education National Meeting (REF-6)
16-20 October 1989; Bariloche Atomic Center; S.C. de Bariloche, Argentina