The group of rigid motions is considered to guide the search for a natural system of space-time coordinates in General Relativity. This search leads us to a natural extension of the space-times that support Painlevé–Gullstrand synchronization. As an interesting example, here we describe a system of rigid coordinates for the cross mode of gravitational linear plane waves.
Lopez, D.; Robles-Hernández, B.; Salud, J.; de la Fuente, M.; Sebastian, N.; Diez, S.; Jaen, J.; Dunmur, D.; Luckhurst , G. Physical chemistry chemical physics Vol. 18, p. 4394-4404 DOI: 10.1039/c5cp07605f Data de publicació: 2016-01-14 Article en revista
We report a calorimetric study of a series of mixtures of two twist-bend liquid crystal dimers, the 1'',7''-bis(4-cyanobiphenyl)-4'-yl heptane (CB7CB) and 1''-(2',4-difluorobiphenyl-4'-yloxy)-9''-(4-cyanobiphenyl-4'-yloxy) nonane (FFO9OCB), the molecules of which have different effective molecular curvatures. High-resolution heat capacity measurements in the vicinity of the NTB-N phase transition for a selected number of binary mixtures clearly indicate a first order NTB-N phase transition for all the investigated mixtures, the strength of which decreases when the nematic range increases. Published theories predict a second order NTB-N phase transition, but we have developed a self-consistent mean field Landau model using two key order parameters: A symmetric and traceless tensor for the orientational order and a short-range vector field which is orthogonal to the helix axis and rotates around of the heliconical structure with an extremely short periodicity. The theory, in its simplified form, depends on two effective elastic constants and explains satisfactorily our heat capacity measurements and also predicts a first-order NTB-N phase transition. In addition, as a complementary source of experimental measurements, the splay (K1) and bend (K3) elastic constants in the conventional nematic phase for the pure compounds and some selected mixtures have been determined.
Physics applets are well known appealing resources to teach and learn physics, and a large number of them are available on the Internet. Nevertheless, not all of them are of the same quality, because such applets do not fit every specific teaching/learning purpose. The start question was which features should have a physics applet in order that it can be considered a good applet according to our experience as teachers or lecturers. The answer should be based on practical evaluations of applets from the Internet, taking quality evaluation criteria already published into account. In this way, an evaluation tool was developed as a rubric which draws attention to the different aspects of an applet that are relevant for teaching or learning a physics topic, grouping these aspects into five categories. Each category is given a separate scoring based on a preparatory qualitative evaluation of the aforementioned aspects. This evaluation tool has been tested on five physics applets by four secondary-school teachers as experts in first-year students’ background. The results show the suitability degree of each of these applets as resources for different teaching/learning environments, as well as the suitability of the evaluation tool itself. In addition, the evaluation tool simplifies the interchange of information on physics applets among teachers and lecturers.
Following on from two recent papers, here we examine the relationship between Newtonian gravitation and general relativity in more depth. This allows us to define a scalar potential which is just the proper time of the vector potential when the latter is interpreted as the geodesic velocity field. The results are closely related to
spacetimes that admit Painlevé–Gullstrand synchronization.
Robles-Hernández, B.; Lopez, D.; de la Fuente, M.; Salud, J.; Sebastian, N.; Diez, S.; Jaen, J.; Dunmur, D.; Luckhurst , G. European Conference on Liquid Crystals p. 48 Data de presentació: 2015-09-10 Presentació treball a congrés
We construct a homothetic covariant Newtonian gravitation theory which unifies inertial homothetic forces and gravitational fields. This is achieved through an equivalence principle based on a local homothetic frame of motion. As a consequence, we can obtain a coherent Newtonian cosmology which admits a cosmological principle and leads to the Friedman equations for a dust universe. Finally we prove that this gravity theory can be obtained as the non-relativistic limit of a class of metrics in General Relativity. The Friedmann–Lemaître–Robertson–Walker metric and its limit are also studied.
A comparative review of the different systems of units that are most usual in electromagnetism leads to the proposal of a new system of units. In this system, the gravitational constant acquires the role of an interaction constant, both for gravitational and electromagnetic interaction, as a result of a redefinition of electric charge. In this way, the new system of units extends in a natural manner to mechanics. The comparison between the gravitational and electromagnetic interactions is of particular relevance.
In an effort to contribute to a better understanding of General Relativity, here we lay the foundations of generalized Newtonian gravity, which unifies inertial forces and gravitational fields. We also formulate a kind of equivalence principle for this generalized Newtonian theory. Finally, we prove that the theory we propose here can be obtained as the non-relativistic limit of General Relativity.
In an effort to contribute to a better understanding of General Relativity,
here we lay the foundations of generalized Newtonian gravity, which unifies inertial
forces and gravitational fields. We also formulate a kind of equivalence principle for
this generalized Newtonian theory. Finally, we prove that the theory we propose here
can be obtained as the non-relativistic limit of General Relativity.
Our first objective was to detect misconceptions about the microscopic nature of sound among senior university students enrolled in different engineering programmes
(from chemistry to telecommunications). We
sought to determine how these misconceptions are expressed (qualitative aspect) and, only very secondarily, to gain a general idea of the extent to which they are held
(quantitative aspect). Our second objective was to explore other misconceptions about wave aspects of sound. We have also considered the degree of consistency in the
model of sound used by each student. Forty students answered a questionnaire including open-ended questions.
Based on their free, spontaneous answers, the main results were as follows: a large majority of students answered most of the questions regarding the microscopic model of
sound according to the scientifically accepted model; however, only a small number answered consistently. The main model misconception found was the notion that sound
is propagated through the travelling of air particles, even in solids. Misconceptions and mental-model inconsistencies tended to depend on the engineering programme in which
the student was enrolled. However, students in general were inconsistent also in applying their model of sound to individual sound properties. The main conclusion is that
our students have not truly internalised the scientifically accepted model that they have allegedly learnt. This implies a need to design learning activities that take these
findings into account in order to be truly efficient.
Audio processors allow to implement laboratory activities specially on acoustics. We have
evaluated three audio processors (Audacity, WaveLab, and Adobe Audition). Although an overall grade was
also calculated as a guideline (not a statement of ‘‘the best’’), the decision about the most suitable one depends on each particular laboratory activity.
In this paper we will describe a Virtual Learning Environment designed to promote selfdirected
learning. We will analyse the results of the opinion survey and evaluation of the
activity developed in the environment. This activity was performed by students without
teacher intervention and it is part of a classroom course of Electromagnetism in the
second year of Industrial and Chemical Engineering. In this particular case it deals with
the concepts related to electrical circuits by applying Kirchhoff’s laws.
En aquesta ponència presentem un Entorn Virtual d’Aprenentatge (EVA) dissenyat per fomentar l’aprenentatge autònom [1,2,3]. Es tracta d’una activitat dirigida en la qual se suggereixen les accions que l’estudiant ha de seguir per aprendre els conceptes relacionats amb la resolució de circuits elèctrics de corrent continu mitjançant l’aplicació de les lleis de Kirchhoff. Aquesta activitat forma part del curs de l’assignatura d’Electromagnetisme de les titulacions d’Enginyeria Industrial i Enginyeria Química de la UPC.
Quan els estudiants van finalitzar l’activitat d’autoaprenentatge proposada, se’ls va demanar de respondre una enquesta d’opinió que ha estat analitzada i valorada.
Pejuan, A.; Bohigas, X.; Jaen, J.; Periago, M.C. Athens Institute for Education and Research - Annual International Conference on Education p. 130 Data de presentació: 2010-05 Presentació treball a congrés
Every planning of an efficient teaching has the aim of achieving satisfactory
learning outcomes. From a constructivistic point of view, it is a commonly
accepted fact that such a planning has to take into account the prior ideas that
students bring to the class. In order to know them, we carried out a survey
about the prior ideas on the nature of sound that our fifteen third-year
engineering students had at the begin of an elective subject on acoustics. We
used a questionnaire where the students had to express their prior ideas with
their own words. Although the students expressed scientifically accepted ideas
in about 2/3 of the individual questions on a whole, a cross comparison
between each student’s answers for the different scenarios revealed a great
number of inconsistencies in the mental model of the nature of sound (wave
model): only about 1/3 of our students were consistent in all these scenarios.
The inconsistency in their reasoning was still clearer when each student had to
apply his/her respective mental model about sound to several properties of
sound, in particular the relationship between pitch and distance travelled by
sound. We analyse the state of the art in the literature about the issue of
students’ consistency, and we consider some proposals suggested in the
literature, which we apply in part in our own teaching resources, in order to
overcome this inconsistency problem.
A course on Basic Acoustics has been implemented as an Internet site with multimedia resources such as Flash animations, video clips, etc. Multimedia resources are particularly suitable for acoustics, due to the special role played by sound. The constructivistic model of learning within the EHEA framework was taken as the most suitable approach. The students’ overall evaluation has been positive, especially as regards the embedded multimedia resources. Furthermore, many comments taken from their evaluations and
assignments have helped to correct deficiencies and to improve the course.
Periago, M.C.; Pejuan, A.; Jaen, J.; Bohigas, X. Annual Conference of the European-Association-for-Education-in-Electrical-and-Information-Engineering p. 52-55 Data de presentació: 2009 Presentació treball a congrés
Periago, M.C.; Pejuan, A.; Jaen, J.; Bohigas, X. Annual Conference of the European-Association-for-Education-in-Electrical-and-Information-Engineering p. 56-61 Data de presentació: 2009 Presentació treball a congrés
Jaen, J.; Bohigas, X.; Novell, M. International Conference GIREP (Groupe International de Recherche sur l'Enseignement de la Physique) p. 1-7 Data de presentació: 2008-08-18 Presentació treball a congrés
Some years ago, it was believed that the learning process would eventually become mostly virtual. ICT tools were
therefore designed with this scenario in mind. Nevertheless, today’s learning process is still predominantly faceto-
face; at most, we have seen a shift towards blended learning. Today we are in the process of incorporating ICT
tools both inside and outside of the classroom. In this paper, we explore how contents—specifically physics
contents—can be used optimally either inside or outside of the classroom.