Tuning Performance of Multi-threaded programs

Diplomityö tarkastelee säikeistettyä ohjelmointia rinnakkaisohjelmoinnin ylemmällä hierarkiatasolla tarkastellen erityisesti hypersäikeistysteknologiaa. Työssä tarkastellaan hypersäikeistyksen hyviä ja huonoja puolia sekä sen vaikutuksia rinnakkaisalgoritmeihin. Työn tavoitteena oli ymmärtää Intel Pentium 4 prosessorin hypersäikeistyksen toteutus ja mahdollistaa sen hyödyntäminen, missä se tuo suorituskyvyllistä etua. Työssä kerättiin ja analysoitiin suorituskykytietoa ajamalla suuri joukko suorituskykytestejä eri olosuhteissa (muistin käsittely, kääntäjän asetukset, ympäristömuuttujat...). Työssä tarkasteltiin kahdentyyppisiä algoritmeja: matriisioperaatioita ja lajittelua. Näissä sovelluksissa on säännöllinen muistinkäyttökuvio, mikä on kaksiteräinen miekka. Se on etu aritmeettis-loogisissa prosessoinnissa, mutta toisaalta huonontaa muistin suorituskykyä. Syynä siihen on nykyaikaisten prosessorien erittäin hyvä raaka suorituskyky säännöllistä dataa käsiteltäessä, mutta muistiarkkitehtuuria rajoittaa välimuistien koko ja useat puskurit. Kun ongelman koko ylittää tietyn rajan, todellinen suorituskyky voi pudota murto-osaan huippusuorituskyvystä.

Software SMEs asStrategic Partners in the Partner Programs of Large International Companies

Tutkielman tavoitteena oli tutkia pienten- ja keskisuurten (PK) ohjelmistoyritysten kansainvälisiä kumppanuuksia. Päätavoitteena oli löytää keinoja kuinka PK-ohjelmistoyritykset voisivat tulla strategisiksi kumppaneksi suurten kansainvälisten yritysten kumppanuusohjelmissa. Lisäksi tutkielmassa oli tavoitteena selvittää kuinka kumppaneiden välistä sitoutumista voitaisiin vahvistaa, jotta PK-ohjelmistoyritykset voisivat saavuttaa todellista lisäarvoa ja kansainvälistä kasvua kumppanuusohjelmien kautta. Tutkielma jakaantuu teoreettiseen ja empiiriseen osaan. Teoreettinen osa keskittyy tarkastelemaan korkean teknologian markkinointia ohjelmistoalalla sekä kansainvälisiä kumppanuuksia. Suurten yritystenkumppanuusohjelmia ei ole tutkittu suomalaisten PK-ohjelmistoyritysten näkökulmasta, minkä vuoksi empiirinen tutkimus on perusteltua. Empiirinen tutkimus toteutettiin laadullisena case-tutkimuksena ja tutkimusmenetelmänä käytettiin puolistrukturoitua haastattelua. Tutkimustulokset osoittavat, että strategisen kumppanin aseman saavuttaminen on pitkä ja haastava matka PK-yrityksille. Suurten kansainvälisten yritysten kumppanuusohjelmat ovat useimmiten monimutkaisia ja todellisen lisäarvon saavuttaminen kumppanuusohjelman kautta vaatii paljon resursseja PK-yrityksiltä. Jotta PK-yritykset voisivat saavuttaa ja säilyttää strategisen kumppanin aseman kumppanuusohjelmassa, vaatii se aktiivista ja päivittäistä vuorovaikutusta kumppaneiden kesken. Erityisesti tiiviit henkilösuhteet oikeiden avainhenkilöiden kanssa ovat välttämättömyys. Läheiset kontaktit mahdollistavat sen, että PK-yritykset voivat ainakin osittain ohittaa kumppanuusohjelman byrokratian, mikä lisää luottamusta ja sitoutumista kumppanuussuhteessa sekä edistää kansainvälistä kasvua ja menestystä liiketoiminnassa.

Data-parallel computation in parallel and distributed environments

The past few decades have seen a considerable increase in the number of parallel and distributed systems. With the development of more complex applications, the need for more powerful systems has emerged and various parallel and distributed environments have been designed and implemented. Each of the environments, including hardware and software, has unique strengths and weaknesses. There is no single parallel environment that can be identified as the best environment for all applications with respect to hardware and software properties. The main goal of this thesis is to provide a novel way of performing data-parallel computation in parallel and distributed environments by utilizing the best characteristics of difference aspects of parallel computing. For the purpose of this thesis, three aspects of parallel computing were identified and studied. First, three parallel environments (shared memory, distributed memory, and a network of workstations) are evaluated to quantify theirsuitability for different parallel applications. Due to the parallel and distributed nature of the environments, networks connecting the processors in these environments were investigated with respect to their performance characteristics. Second, scheduling algorithms are studied in order to make them more efficient and effective. A concept of application-specific information scheduling is introduced. The application- specific information is data about the workload extractedfrom an application, which is provided to a scheduling algorithm. Three scheduling algorithms are enhanced to utilize the application-specific information to further refine their scheduling properties. A more accurate description of the workload is especially important in cases where the workunits are heterogeneous and the parallel environment is heterogeneous and/or non-dedicated. The results obtained show that the additional information regarding the workload has a positive impact on the performance of applications. Third, a programming paradigm for networks of symmetric multiprocessor (SMP) workstations is introduced. The MPIT programming paradigm incorporates the Message Passing Interface (MPI) with threads to provide a methodology to write parallel applications that efficiently utilize the available resources and minimize the overhead. The MPIT allows for communication and computation to overlap by deploying a dedicated thread for communication. Furthermore, the programming paradigm implements an application-specific scheduling algorithm. The scheduling algorithm is executed by the communication thread. Thus, the scheduling does not affect the execution of the parallel application. Performance results achieved from the MPIT show that considerable improvements over conventional MPI applications are achieved.

Introducing massively parallel computers into operational weather forecasting

Numerical weather prediction and climate simulation have been among the computationally most demanding applications of high performance computing eversince they were started in the 1950's. Since the 1980's, the most powerful computers have featured an ever larger number of processors. By the early 2000's, this number is often several thousand. An operational weather model must use all these processors in a highly coordinated fashion. The critical resource in running such models is not computation, but the amount of necessary communication between the processors. The communication capacity of parallel computers often fallsfar short of their computational power. The articles in this thesis cover fourteen years of research into how to harness thousands of processors on a single weather forecast or climate simulation, so that the application can benefit as much as possible from the power of parallel high performance computers. The resultsattained in these articles have already been widely applied, so that currently most of the organizations that carry out global weather forecasting or climate simulation anywhere in the world use methods introduced in them. Some further studies extend parallelization opportunities into other parts of the weather forecasting environment, in particular to data assimilation of satellite observations.

Verkkokäyttöisten tahtimoottorien käynnistyshäiriön tutkiminen

Diplomityössä tutkitaan verkkokäyttöisten harjattomasti magnetoitujen tahtimoottorien käynnistyshäiriötä, jossa moottori magnetoituu vasta useiden sekuntien kuluttua magnetoinnin kytkemisestä magnetointilaitteiston normaalista toiminnasta huolimatta. Syy magnetoitumisen viivästymiseen on magnetointikoneen oikosulkeutuminen roottorin ylijännitesuojana toimivan tyristorihaaran kautta siitä huolimatta, että tyristorihaaran tyristorien on tarkoitus olla johtamattomassa tilassa magnetointikoneen alkaessa syöttää magnetointivirtaa. Syitä tyristorien johtavana pysymiseen magnetoinnin kytkennän jälkeen etsitään tahtimoottorin käynnistyskokeista saatujen mittaustulosten sekä SMT- ja FCSMEK-laskentaohjelmilla tehtyjen käynnistyssimulointien avulla. Samalla arvioidaan ohjelmien käyttökelpoisuutta käynnistyshäiriön ennakoimisessa. Diplomityössä esitetään syyt kahden esimerkkikoneen magnetoitumisen viivästymiseen sekä muutoksia roottoripiiriin ja käynnistysproseduuriin, joiden avulla tutkittu käynnistyshäiriö voitaisiin tulevaisuudessa todennäköisesti välttää.

Evaluation of Teacher Education Programs by Students and Graduates

The purpose of this research was to do a repeated cross-sectional research on class teachers who study in the 4th year and also graduated at the Faculty of Education, University of Turku between the years of 2000 through 2004. Specifically, seven research questions were addressed to target the main purpose of the study: How do class teacher education masters’ degree senior students and graduates rate “importance; effectiveness; and quality” of training they have received at the Faculty of Education? Are there significant differences between overall ratings of importance; effectiveness and quality of training by year of graduation, sex, and age (for graduates) and sex and age (for senior students)? Is there significant relationship between respondents’ overall ratings of importance; effectiveness and their overall ratings of the quality of training and preparation they have received? Are there significant differences between graduates and senior students about importance, effectiveness, and quality of teacher education programs? And what do teachers’ [Graduates] believe about how increasing work experience has changed their opinions of their preservice training? Moreover the following concepts related to the instructional activities were studied: critical thinking skills, communication skills, attention to ethics, curriculum and instruction (planning), role of teacher and teaching knowledge, assessment skills, attention to continuous professional development, subject matters knowledge, knowledge of learning environment, and using educational technology. Researcher also tried to find influence of some moderator variables e.g. year of graduation, sex, and age on the dependent and independent variables. This study consisted of two questionnaires (a structured likert-scale and an open ended questionnaire). The population in study 1 was all senior students and 2000-2004 class teacher education masters’ degree from the departments of Teacher Education Faculty of Education at University of Turku. Of the 1020 students and graduates the researcher was able to find current addresses of 675 of the subjects and of the 675 graduates contacted, 439 or 66.2 percent responded to the survey. The population in study 2 was all class teachers who graduated from Turku University and now work in the few basic schools (59 Schools) in South- West Finland. 257 teachers answered to the open ended web-based questions. SPSS was used to produce standard deviations; Analysis of Variance; Pearson Product Moment Correlation (r); T-test; ANOVA, Bonferroni post-hoc test; and Polynomial Contrast tests meant to analyze linear trend. An alpha level of .05 was used to determine statistical significance. The results of the study showed that: A majority of the respondents (graduates and students) rated the overall importance, effectiveness and quality of the teacher education programs as important, effective and good. Generally speaking there were only a few significant differences between the cohorts and groups related to the background variables (gender, age). The different cohorts were rating the quality of the programs very similarly but some differences between the cohorts were found in the importance and effectiveness ratings. Graduates of 2001 and 2002 rated the importance of the program significantly higher than 2000 graduates. The effectiveness of the programs was rated significantly higher by 2001 and 2003 graduates than other groups. In spite of these individual differences between cohorts there were no linear trends among the year cohorts in any measure. In respondents’ ratings of the effectiveness of teacher education programs there was significant difference between males and females; females rated it higher than males. There were no significant differences between males’ and females’ ratings of the importance and quality of programs. In the ratings there was only one difference between age groups. Older graduates (35 years or older) rated the importance of the teacher training significantly higher that 25-35 years old graduates. In graduates’ ratings there were positive but relatively low correlations between all variables related to importance, effectiveness and quality of Teacher Education Programs. Generally speaking students’ ratings about importance, effectiveness and quality of teacher education program were very positive. There was only one significant difference related to the background variables. Females rated higher the effectiveness of the program. The comparison of students’ and graduates’ perception about importance, effectiveness, and quality of teacher education programs showed that there were no significant differences between graduates and students in the overall ratings. However there were differences in some individual variables. Students rated higher in importance of “Continuous Professional Development”, effectiveness of “Critical Thinking Skills” and “Using Educational Technology” and quality of “Advice received from the advisor”. Graduates rated higher in importance of “Knowledge of Learning Environment” and effectiveness of “Continuous Professional Development”. According to the qualitative data of study 2 some graduates expressed that their perceptions have not changed about the importance, effectiveness, and quality of training that they received during their study time. They pointed out that teacher education programs have provided them the basic theoretical/formal knowledge and some training of practical routines. However, a majority of the teachers seems to have somewhat critical opinions about the teacher education. These teachers were not satisfied with teacher education programs because they argued that the programs failed to meet their practical demands in different everyday situations of the classroom e.g. in coping with students’ learning difficulties, multiprofessional communication with parents and other professional groups (psychologists and social workers), and classroom management problems. Participants also emphasized more practice oriented knowledge of subject matter, evaluation methods and teachers’ rights and responsibilities. Therefore, they (54.1% of participants) suggested that teacher education departments should provide more practice-based courses and programs as well as closer collaboration between regular schools and teacher education departments in order to fill gap between theory and practice.

Developing of the Variable Speed Drive -control in simulated parallel pumping systems

This thesis presents briefly the basic operation and use of centrifugal pumps and parallel pumping applications. The characteristics of parallel pumping applications are compared to circuitry, in order to search analogy between these technical fields. The purpose of studying circuitry is to find out if common software tools for solving circuit performance could be used to observe parallel pumping applications. The empirical part of the thesis introduces a simulation environment for parallel pumping systems, which is based on circuit components of Matlab Simulink —software. The created simulation environment ensures the observation of variable speed controlled parallel pumping systems in case of different controlling methods. The introduced simulation environment was evaluated by building a simulation model for actual parallel pumping system at Lappeenranta University of Technology. The simulated performance of the parallel pumps was compared to measured values of the actual system. The gathered information shows, that if the initial data of the system and pump perfonnance is adequate, the circuitry based simulation environment can be exploited to observe parallel pumping systems. The introduced simulation environment can represent the actual operation of parallel pumps in reasonably accuracy. There by the circuitry based simulation can be used as a researching tool to develop new controlling ways for parallel pumps.

Facilitating coordination improvement efforts in cross-functional process development programs

Business process improvement is a common approach in increasing the effectiveness of an organization. It can be seen as an effort to increase coordination between units. Process improvement has proved to be challenging, and most management consultation firms facilitate organizations in this kind of initiatives. Cross-functional improvement is one of the main areas for internal consultants as well. However, the needs, challenges and means of cross-functional help have been rarely discussed in the literature. The objective of this thesis is on one hand to present a conceptual and descriptive framework to help understand the challenges of facilitating coordination improvement efforts in cross-functional improvement programs, and on the other hand to develop and test feasible solutions for some facilitation situations. The research questions are: 1. Why and in what kind of situations do organizations need help in developing coordination in cross-functional processes? 2. How can a facilitator help organizations in improving coordination to develop cross-functional processes? The study consists of two parts. The first part is an overview of the dissertation, and the second part comprises six research publications. The theoretical background for the study are the differentiation causing challenges in cross-functional settings, the coordination needed to improve processes, change management principles, methods and tools, and consultation practises. Three of the publications introduce tools for helping in developing prerequisites, planning responsibilities and supporting learning during the cross-functional program. The three other papers present frameworks to help understand and analyse the improvement situation. The main methodological approaches used in this study are design science research, action research and case research. The research data has been collected from ten cases representing different kinds of organizations, processes and developing situations. The data has been collected mainly by observation, semi-structured interviews and questionnaires. The research contributes to the rare literature combining coordination theories and process improvement practises. It also provides additional understanding of a holistic point of view in process improvement situations. The most important contribution is the addition to the theories of facilitating change in process improvement situations. From the managerial point of view, this study gives advice to managers and consultants in planning and executing cross-functional programs. The main factors increasing the need for facilitation are the challenges for differentiation, challenges of organizational change in general, and the novelty of initiatives and improvement practices concerning process development. Organizations need help in creating the prerequisites to change, in planning initiatives, easing conflict management and collaboration between groups, as well as supporting the learning of cross-functional improvement. The main challenges of facilitation are combining the different roles as a consultant, maintaining the ownership for the improvement project with the client, and supporting learning in the client organization.

Characterisation of pigment particles by scanning electron microscope and image analysis programs

Coating and filler pigments have strong influence to the properties of the paper. Filler content can be even over 30 % and pigment content in coating is about 85-95 weight percent. The physical and chemical properties of the pigments are different and the knowledge of these properties is important for optimising of optical and printing properties of the paper. The size and shape of pigment particles can be measured by different analysers which can be based on sedimentation, laser diffraction, changes in electric field etc. In this master's thesis was researched particle properties especially by scanning electron microscope (SEM) and image analysis programs. Research included nine pigments with different particle size and shape. Pigments were analysed by two image analysis programs (INCA Feature and Poikki), Coulter LS230 (laser diffraction) and SediGraph 5100 (sedimentation). The results were compared to perceive the effect of particle shape to the performance of the analysers. Only image analysis programs gave parameters of the particle shape. One part of research was also the sample preparation for SEM. Individual particles should be separated and distinct in ideal sample. Analysing methods gave different results but results from image analysis programs corresponded even to sedimentation or to laser diffraction depending on the particle shape. Detailed analysis of the particle shape required high magnification in SEM, but measured parameters described very well the shape of the particles. Large particles (ecd~1 µm) could be used also in 3D-modelling which enabled the measurement of the thickness of the particles. Scanning electron microscope and image analysis programs were effective and multifunctional tools for particle analyses. Development and experience will devise the usability of analysing method in routine use.

Error Modeling and Accuracy Analysis of a Novel Mobile Hybrid Parallel Robot

Over the last decades, calibration techniques have been widely used to improve the accuracy of robots and machine tools since they only involve software modification instead of changing the design and manufacture of the hardware. Traditionally, there are four steps are required for a calibration, i.e. error modeling, measurement, parameter identification and compensation. The objective of this thesis is to propose a method for the kinematics analysis and error modeling of a newly developed hybrid redundant robot IWR (Intersector Welding Robot), which possesses ten degrees of freedom (DOF) where 6-DOF in parallel and additional 4-DOF in serial. In this article, the problem of kinematics modeling and error modeling of the proposed IWR robot are discussed. Based on the vector arithmetic method, the kinematics model and the sensitivity model of the end-effector subject to the structure parameters is derived and analyzed. The relations between the pose (position and orientation) accuracy and manufacturing tolerances, actuation errors, and connection errors are formulated. Computer simulation is performed to examine the validity and effectiveness of the proposed method.

The Pursued Benefits of Customer Loyalty Programs

Customer loyalty programs have increased in recent decades and customers are members in several loyalty programs. Loyalty programs are seen as a tool of exploiting customer relationship management with the aim of long-term, profitable customer relationships. Companies have created such a market where customers are rewarded automatically, even if they are disloyal. In addition, companies are struggling as they try to motivate customers to purchase more and make more frequent visits.

Parallel-Operating Three-Phase Voltage Source Inverters – Circulating CurrentModeling, Analysis and Mitigation

The maximum realizable power throughput of power electronic converters may be limited or constrained by technical or economical considerations. One solution to this problemis to connect several power converter units in parallel. The parallel connection can be used to increase the current carrying capacity of the overall system beyond the ratings of individual power converter units. Thus, it is possible to use several lower-power converter units, produced in large quantities, as building blocks to construct high-power converters in a modular manner. High-power converters realized by using parallel connection are needed for example in multimegawatt wind power generation systems. Parallel connection of power converter units is also required in emerging applications such as photovoltaic and fuel cell power conversion. The parallel operation of power converter units is not, however, problem free. This is because parallel-operating units are subject to overcurrent stresses, which are caused by unequal load current sharing or currents that flow between the units. Commonly, the term ’circulatingcurrent’ is used to describe both the unequal load current sharing and the currents flowing between the units. Circulating currents, again, are caused by component tolerances and asynchronous operation of the parallel units. Parallel-operating units are also subject to stresses caused by unequal thermal stress distribution. Both of these problemscan, nevertheless, be handled with a proper circulating current control. To design an effective circulating current control system, we need information about circulating current dynamics. The dynamics of the circulating currents can be investigated by developing appropriate mathematical models. In this dissertation, circulating current models aredeveloped for two different types of parallel two-level three-phase inverter configurations. Themodels, which are developed for an arbitrary number of parallel units, provide a framework for analyzing circulating current generation mechanisms and developing circulating current control systems. In addition to developing circulating current models, modulation of parallel inverters is considered. It is illustrated that depending on the parallel inverter configuration and the modulation method applied, common-mode circulating currents may be excited as a consequence of the differential-mode circulating current control. To prevent the common-mode circulating currents that are caused by the modulation, a dual modulator method is introduced. The dual modulator basically consists of two independently operating modulators, the outputs of which eventually constitute the switching commands of the inverter. The two independently operating modulators are referred to as primary and secondary modulators. In its intended usage, the same voltage vector is fed to the primary modulators of each parallel unit, and the inputs of the secondary modulators are obtained from the circulating current controllers. To ensure that voltage commands obtained from the circulating current controllers are realizable, it must be guaranteed that the inverter is not driven into saturation by the primary modulator. The inverter saturation can be prevented by limiting the inputs of the primary and secondary modulators. Because of this, also a limitation algorithm is proposed. The operation of both the proposed dual modulator and the limitation algorithm is verified experimentally.

Permanent Magnet Synchronous Machine for Parallel Hybrid Vehicle

The aim of this thesis is to describe hybrid drive design problems, the advantages and difficulties related to the drive. A review of possible hybrid constructions, benefits of parallel, series and series-parallel hybrids is done. In the thesis analytical and finite element calculations of permanent magnet synchronous machines with embedded magnets were done. The finite element calculations were done using Cedrat’s Flux 2D software. This machine is planned to be used as a motor-generator in a low power parallel hybrid vehicle. The boundary conditions for the design were found from Lucas-TVS Ltd., India. Design Requirements, briefly: • The system DC voltage level is 120 V, which implies Uphase = 49 V (RMS) in a three phase system. • The power output of 10 kW at base speed 1500 rpm (Torque of 65 Nm) is desired. • The maximum outer diameter should not be more than 250 mm, and the maximum core length should not exceed 40 mm. The main difficulties which the author met were the dimensional restrictions. After having designed and analyzed several possible constructions they were compared and the final design selected. Dimensioned and detailed design is performed. Effects of different parameters, such as the number of poles, number of turns and magnetic geometry are discussed. The best modification offers considerable reduction of volume.

Parallella, dynamiska representationer i gymnasiefysiken : implementering av ett interaktivt datorverktyg i didaktiska situationer och uppfattning av effektivt lärande

The computer is a useful tool in the teaching of upper secondary school physics, and should not have a subordinate role in students' learning process. However, computers and computer-based tools are often not available when they could serve their purpose best in the ongoing teaching. Another problem is the fact that commercially available tools are not usable in the way the teacher wants. The aim of this thesis was to try out a novel teaching scenario in a complicated subject in physics, electrodynamics. The didactic engineering of the thesis consisted of developing a computer-based simulation and training material, implementing the tool in physics teaching and investigating its effectiveness in the learning process. The design-based research method, didactic engineering (Artigue, 1994), which is based on the theoryof didactical situations (Brousseau, 1997), was used as a frame of reference for the design of this type of teaching product. In designing the simulation tool a general spreadsheet program was used. The design was based on parallel, dynamic representations of the physics behind the function of an AC series circuit in both graphical and numerical form. The tool, which was furnished with possibilities to control the representations in an interactive way, was hypothesized to activate the students and promote the effectiveness of their learning. An effect variable was constructed in order to measure the students' and teachers' conceptions of learning effectiveness. The empirical study was twofold. Twelve physics students, who attended a course in electrodynamics in an upper secondary school, participated in a class experiment with the computer-based tool implemented in three modes of didactical situations: practice, concept introduction and assessment. The main goal of the didactical situations was to have students solve problems and study the function of AC series circuits, taking responsibility for theirown learning process. In the teacher study eighteen Swedish speaking physics teachers evaluated the didactic potential of the computer-based tool and the accompanying paper-based material without using them in their physics teaching. Quantitative and qualitative data were collected using questionnaires, observations and interviews. The result of the studies showed that both the group of students and the teachers had generally positive conceptions of learning effectiveness. The students' conceptions were more positive in the practice situation than in the concept introduction situation, a setting that was more explorative. However, it turned out that the students' conceptions were also positive in the more complex assessment situation. This had not been hypothesized. A deeper analysis of data from observations and interviews showed that one of the students in each pair was more active than the other, taking more initiative and more responsibilityfor the student-student and student-computer interaction. These active studentshad strong, positive conceptions of learning effectiveness in each of the threedidactical situations. The group of less active students had a weak but positive conception in the first iv two situations, but a negative conception in the assessment situation, thus corroborating the hypothesis ad hoc. The teacher study revealed that computers were seldom used in physics teaching and that computer programs were in short supply. The use of a computer was considered time-consuming. As long as physics teaching with computer-based tools has to take place in special computer rooms, the use of such tools will remain limited. The affordance is enhanced when the physical dimensions as well as the performance of the computer are optimised. As a consequence, the computer then becomes a real learning tool for each pair of students, smoothly integrated into the ongoing teaching in the same space where teaching normally takes place. With more interactive support from the teacher, the computer-based parallel, dynamic representations will be efficient in promoting the learning process of the students with focus on qualitative reasoning - an often neglected part of the learning process of the students in upper secondary school physics.