Lucien Lemmens - Academia.edu (original) (raw)

Papers by Lucien Lemmens

Research paper thumbnail of Thermal conductivity of some soliton-bearing magnetic systems

Research paper thumbnail of Recent developments in condensed matter physics, vol. 1, invited papers

Materials Research Bulletin, 1982

Research paper thumbnail of An ideal mixture of N confined S=1-bosons

Physica B-condensed Matter, 2000

Using a new method – Path integral approach to Many Body theory – we obtain the free energy for a... more Using a new method – Path integral approach to Many Body theory – we obtain the free energy for a finite number of bosons, confined in a harmonic potential and having spin states with a different energy characterised by a magnetic quantum number. It is seen that all internal states prefer a unique condensate attributed to the (high temperature) maximum in the specific heat, the second (very low temperature) maximum is identified as the Schottky anomaly, coming from lifting the degeneracy of the internal degrees of freedom. The susceptibility clearly demonstrates the dependence of the condensation temperature on the energies of the internal degrees of freedom.

Research paper thumbnail of Relations between various dynamical local field corrections in the dielectric function

Physica Status Solidi (a), 1980

ABSTRACT

Research paper thumbnail of Dielectric function of the electron gas with dynamical-exchange decoupling. I. Analytical treatment

Physical Review B, 1980

Dynamical-exchange effects in the dielectric function of the electron gas can be described by a f... more Dynamical-exchange effects in the dielectric function of the electron gas can be described by a frequency-dependent local-field correction G(q,ω). In an earlier derivation, we deduced an explicit expression for G(q,ω) as a sixfold integral, which was obtained from the ...

Research paper thumbnail of Confined harmonically interacting spin-polarized fermions

Physical Review E, 1998

The thermodynamical properties are calculated for a three-dimensional model of N harmonically int... more The thermodynamical properties are calculated for a three-dimensional model of N harmonically interacting spin-polarized fermions in a parabolic potential well. The obtained dependences of the chemical potential and of the internal energy on the complete range of the temperature and of the number of particles turn out to obey a scaling law, similar to the scaling from the continuum approximation

Research paper thumbnail of Thermal Conductivity in the Soliton Bearing Ferromagnetic System Chab

Le Journal de Physique Colloques, 1988

The thermal conductivity of [C6H11NH3] CuBr3 (CHAB) has been measured in the region 1.5 K <T < 10... more The thermal conductivity of [C6H11NH3] CuBr3 (CHAB) has been measured in the region 1.5 K <T < 10 K and B < 7 T. Comparison of the data with a model describing the heat conduction by magnons and solitons shows a systematic deviation,.most likely due to the neglect of heat transport by the phonon system.

Research paper thumbnail of Probability assignment in a quantum statistical model

The evolution of a quantum system, appropriate to describe nano-magnets, can be mapped on a Marko... more The evolution of a quantum system, appropriate to describe nano-magnets, can be mapped on a Markov process, continuous in beta\betabeta. The mapping implies a probability assignment that can be used to study the probability density (PDF) of the magnetization. This procedure is not the common way to assign probabilities, usually an assignment that is compatible with the von Neumann entropy is made. Making these two assignments for the same system and comparing both PDFs, we see that they differ numerically. In other words the assignments lead to different PDFs for the same observable within the same model for the dynamics of the system. Using the maximum entropy principle we show that the assignment resulting from the mapping on the Markov process makes less assumptions than the other one. Using a stochastic queue model that can be mapped on a quantum statistical model, we control both assignments on compatibility with the Gibbs procedure for systems in thermal equilibrium and argue that t...

Research paper thumbnail of Electron phonon induced cyclotron resonance

Solid State Communications, 1974

ABSTRACT

Research paper thumbnail of Frequency-Dependent Exchange Correction to the Dielectric Function of the Electron Gas

Physica Status Solidi B-basic Solid State Physics, 1976

The equation of motion of the Wigner distribution function in the homogeneous electron gas is dec... more The equation of motion of the Wigner distribution function in the homogeneous electron gas is decoupled using the Hartree-Fock prescription. After linearization, the variational procedure, used by Rajagopal and Jain and by Langreth is applied. The transverse and the longitudinal dielectric functions in the Hartree-Fock approximation are derived, and the consistency of the equations for the charge density and the current density is examined. Several limits are calculated. The slope of the plasmon mode is substantially lowered by the exchange interactions, and the damped acoustic mode disappears for the densities that give a negative bulk modulus in the Hartree-Fock approximation. The exchange interaction only slightly influences the dispersion of the transverse collective modes. Mittels der Hartree-Fock-Vorschrift wird die Bewegungsgleichung der Wigner-Verteihngsfunktion im homogenen Elektronengas entkoppelt. Nach Linearisierung wird die von Rajagopal und Jain sowie von Langreth benutzte Variationsmethode angewendet. Es werden die transversalen und longitudinalen dielektrischen Funktionen in der Hartree-Pock-Naherung abgeleitet und die Konsistenz der Gleichungen fur die Ladungsdichte und Stromdichte untersucht. Einige Grenzfille werden berechnet. Der Anstieg der Plasmon-Mode wird durch die Austauschwechselwirkungen wesentlich verringert, und die gediimpfte akustische Mode verschwindet fur die Dichten, die einen negativen Kompressionsmodul in der Hartree-Fock-Niherung liefern. Die Austauschwechselwirkung beeinflul3t die Dispersion der kollektiven transversalen Moden nur wenig.

Research paper thumbnail of Classical aspects of quantum spin chains (abstract)

A variational estimate of the free energy of a quantum spin chain based on the stochastic behavio... more A variational estimate of the free energy of a quantum spin chain based on the stochastic behavior of the quantization axes is proposed. It allows a description of the nonlinear excitations and quantum spin waves within the same framework.For an easy-plane ferromagnet with an external field in the plane it reveals that the nonlinear excitations (solitons) are predominantly described by the classical degrees of freedom. Considerable effort has been devoted to the theoretical description1 and experimental verification of the existence of nonlinear excitations. In this field magnetic chain systems have played an important part.2 Chain systems with an easy-plane anisotropy, such as (C6 H11 NH3 )CuBr3 (CHAB) and CsNiF3 , which are subjected to a symmetry breaking field, were found to be soliton bearing.3 Theoretically the description of the nonlinear effect is based on the mapping of the spin dynamics on a sine-Gordon model. Further research4 indicated that the interpretation of the ther...

Research paper thumbnail of Quantum canonical ensemble: a projection operator approach

Fixing the number of particles N, the quantum canonical ensemble imposes a constraint on the occu... more Fixing the number of particles N, the quantum canonical ensemble imposes a constraint on the occupation numbers of single-particle states. The constraint particularly hampers the systematic calculation of the partition function and any relevant thermodynamic expectation value for arbitrary N since, unlike the case of the grand-canonical ensemble, traces in the N-particle Hilbert space fail to factorize into simple traces over single-particle states. In this paper we introduce a projection operator that enables a constraint-free computation of the partition function and its derived quantities, at the price of an angular or contour integration. Being applicable to both bosonic and fermionic systems in arbitrary dimensions, the projection operator approach provides transparent integral representations for the partition function Z N and the Helmholtz free energy F N as well as for two-and four-point correlation functions. While appearing only as a secondary quantity in the present context, the chemical potential emerges as a by-product from the relation µ N = F N+1 − F N , as illustrated for a two-dimensional fermion gas with N ranging between 2 and 500.

Research paper thumbnail of Quality Control in Small Groups

The smallness of some groups in a set up to control the quality of a service using questionnaires... more The smallness of some groups in a set up to control the quality of a service using questionnaires limits the size of the samples, this limitation has several consequences. Indeed the common approach used for relatively large groups, based on the central limit theorem and the law of large numbers, cannot be used anymore to construct estimators for the parameters of the model. Using an inverse probability will lift these restrictions.

Research paper thumbnail of Quality Control in Small Groups

The smallness of some groups in a set up to control the quality of a service using questionnaires... more The smallness of some groups in a set up to control the quality of a service using questionnaires limits the size of the samples, this limitation has several consequences. Indeed the common approach used for relatively large groups, based on the central limit theorem and the law of large numbers, cannot be used anymore to construct estimators for the parameters of the model. Using an inverse probability will lift these restrictions.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of Frequency dependent conductivity tensor for polarons in a magnetic field

Research paper thumbnail of Thermodynamics and Path Integrals for Identical Particles: The Formalism

International Journal of Modern Physics B

A generalization of symmetrized density matrices in combination with the technique of generating ... more A generalization of symmetrized density matrices in combination with the technique of generating functions allows to calculate the partition function and the static correlation functions of identical particles in a parabolic confining well with harmonic two-body interactions.

Research paper thumbnail of Thermal conductivity of some soliton-bearing magnetic systems

Research paper thumbnail of Recent developments in condensed matter physics, vol. 1, invited papers

Materials Research Bulletin, 1982

Research paper thumbnail of An ideal mixture of N confined S=1-bosons

Physica B-condensed Matter, 2000

Using a new method – Path integral approach to Many Body theory – we obtain the free energy for a... more Using a new method – Path integral approach to Many Body theory – we obtain the free energy for a finite number of bosons, confined in a harmonic potential and having spin states with a different energy characterised by a magnetic quantum number. It is seen that all internal states prefer a unique condensate attributed to the (high temperature) maximum in the specific heat, the second (very low temperature) maximum is identified as the Schottky anomaly, coming from lifting the degeneracy of the internal degrees of freedom. The susceptibility clearly demonstrates the dependence of the condensation temperature on the energies of the internal degrees of freedom.

Research paper thumbnail of Relations between various dynamical local field corrections in the dielectric function

Physica Status Solidi (a), 1980

ABSTRACT

Research paper thumbnail of Dielectric function of the electron gas with dynamical-exchange decoupling. I. Analytical treatment

Physical Review B, 1980

Dynamical-exchange effects in the dielectric function of the electron gas can be described by a f... more Dynamical-exchange effects in the dielectric function of the electron gas can be described by a frequency-dependent local-field correction G(q,ω). In an earlier derivation, we deduced an explicit expression for G(q,ω) as a sixfold integral, which was obtained from the ...

Research paper thumbnail of Confined harmonically interacting spin-polarized fermions

Physical Review E, 1998

The thermodynamical properties are calculated for a three-dimensional model of N harmonically int... more The thermodynamical properties are calculated for a three-dimensional model of N harmonically interacting spin-polarized fermions in a parabolic potential well. The obtained dependences of the chemical potential and of the internal energy on the complete range of the temperature and of the number of particles turn out to obey a scaling law, similar to the scaling from the continuum approximation

Research paper thumbnail of Thermal Conductivity in the Soliton Bearing Ferromagnetic System Chab

Le Journal de Physique Colloques, 1988

The thermal conductivity of [C6H11NH3] CuBr3 (CHAB) has been measured in the region 1.5 K <T < 10... more The thermal conductivity of [C6H11NH3] CuBr3 (CHAB) has been measured in the region 1.5 K <T < 10 K and B < 7 T. Comparison of the data with a model describing the heat conduction by magnons and solitons shows a systematic deviation,.most likely due to the neglect of heat transport by the phonon system.

Research paper thumbnail of Probability assignment in a quantum statistical model

The evolution of a quantum system, appropriate to describe nano-magnets, can be mapped on a Marko... more The evolution of a quantum system, appropriate to describe nano-magnets, can be mapped on a Markov process, continuous in beta\betabeta. The mapping implies a probability assignment that can be used to study the probability density (PDF) of the magnetization. This procedure is not the common way to assign probabilities, usually an assignment that is compatible with the von Neumann entropy is made. Making these two assignments for the same system and comparing both PDFs, we see that they differ numerically. In other words the assignments lead to different PDFs for the same observable within the same model for the dynamics of the system. Using the maximum entropy principle we show that the assignment resulting from the mapping on the Markov process makes less assumptions than the other one. Using a stochastic queue model that can be mapped on a quantum statistical model, we control both assignments on compatibility with the Gibbs procedure for systems in thermal equilibrium and argue that t...

Research paper thumbnail of Electron phonon induced cyclotron resonance

Solid State Communications, 1974

ABSTRACT

Research paper thumbnail of Frequency-Dependent Exchange Correction to the Dielectric Function of the Electron Gas

Physica Status Solidi B-basic Solid State Physics, 1976

The equation of motion of the Wigner distribution function in the homogeneous electron gas is dec... more The equation of motion of the Wigner distribution function in the homogeneous electron gas is decoupled using the Hartree-Fock prescription. After linearization, the variational procedure, used by Rajagopal and Jain and by Langreth is applied. The transverse and the longitudinal dielectric functions in the Hartree-Fock approximation are derived, and the consistency of the equations for the charge density and the current density is examined. Several limits are calculated. The slope of the plasmon mode is substantially lowered by the exchange interactions, and the damped acoustic mode disappears for the densities that give a negative bulk modulus in the Hartree-Fock approximation. The exchange interaction only slightly influences the dispersion of the transverse collective modes. Mittels der Hartree-Fock-Vorschrift wird die Bewegungsgleichung der Wigner-Verteihngsfunktion im homogenen Elektronengas entkoppelt. Nach Linearisierung wird die von Rajagopal und Jain sowie von Langreth benutzte Variationsmethode angewendet. Es werden die transversalen und longitudinalen dielektrischen Funktionen in der Hartree-Pock-Naherung abgeleitet und die Konsistenz der Gleichungen fur die Ladungsdichte und Stromdichte untersucht. Einige Grenzfille werden berechnet. Der Anstieg der Plasmon-Mode wird durch die Austauschwechselwirkungen wesentlich verringert, und die gediimpfte akustische Mode verschwindet fur die Dichten, die einen negativen Kompressionsmodul in der Hartree-Fock-Niherung liefern. Die Austauschwechselwirkung beeinflul3t die Dispersion der kollektiven transversalen Moden nur wenig.

Research paper thumbnail of Classical aspects of quantum spin chains (abstract)

A variational estimate of the free energy of a quantum spin chain based on the stochastic behavio... more A variational estimate of the free energy of a quantum spin chain based on the stochastic behavior of the quantization axes is proposed. It allows a description of the nonlinear excitations and quantum spin waves within the same framework.For an easy-plane ferromagnet with an external field in the plane it reveals that the nonlinear excitations (solitons) are predominantly described by the classical degrees of freedom. Considerable effort has been devoted to the theoretical description1 and experimental verification of the existence of nonlinear excitations. In this field magnetic chain systems have played an important part.2 Chain systems with an easy-plane anisotropy, such as (C6 H11 NH3 )CuBr3 (CHAB) and CsNiF3 , which are subjected to a symmetry breaking field, were found to be soliton bearing.3 Theoretically the description of the nonlinear effect is based on the mapping of the spin dynamics on a sine-Gordon model. Further research4 indicated that the interpretation of the ther...

Research paper thumbnail of Quantum canonical ensemble: a projection operator approach

Fixing the number of particles N, the quantum canonical ensemble imposes a constraint on the occu... more Fixing the number of particles N, the quantum canonical ensemble imposes a constraint on the occupation numbers of single-particle states. The constraint particularly hampers the systematic calculation of the partition function and any relevant thermodynamic expectation value for arbitrary N since, unlike the case of the grand-canonical ensemble, traces in the N-particle Hilbert space fail to factorize into simple traces over single-particle states. In this paper we introduce a projection operator that enables a constraint-free computation of the partition function and its derived quantities, at the price of an angular or contour integration. Being applicable to both bosonic and fermionic systems in arbitrary dimensions, the projection operator approach provides transparent integral representations for the partition function Z N and the Helmholtz free energy F N as well as for two-and four-point correlation functions. While appearing only as a secondary quantity in the present context, the chemical potential emerges as a by-product from the relation µ N = F N+1 − F N , as illustrated for a two-dimensional fermion gas with N ranging between 2 and 500.

Research paper thumbnail of Quality Control in Small Groups

The smallness of some groups in a set up to control the quality of a service using questionnaires... more The smallness of some groups in a set up to control the quality of a service using questionnaires limits the size of the samples, this limitation has several consequences. Indeed the common approach used for relatively large groups, based on the central limit theorem and the law of large numbers, cannot be used anymore to construct estimators for the parameters of the model. Using an inverse probability will lift these restrictions.

Research paper thumbnail of Quality Control in Small Groups

The smallness of some groups in a set up to control the quality of a service using questionnaires... more The smallness of some groups in a set up to control the quality of a service using questionnaires limits the size of the samples, this limitation has several consequences. Indeed the common approach used for relatively large groups, based on the central limit theorem and the law of large numbers, cannot be used anymore to construct estimators for the parameters of the model. Using an inverse probability will lift these restrictions.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Journal of Marine Science and Technology, 2014

ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks o... more ABSTRACT Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.

Research paper thumbnail of Frequency dependent conductivity tensor for polarons in a magnetic field

Research paper thumbnail of Thermodynamics and Path Integrals for Identical Particles: The Formalism

International Journal of Modern Physics B

A generalization of symmetrized density matrices in combination with the technique of generating ... more A generalization of symmetrized density matrices in combination with the technique of generating functions allows to calculate the partition function and the static correlation functions of identical particles in a parabolic confining well with harmonic two-body interactions.