The ability to solve physics problems in symbolic and numeric representations

The aim of this study is to analyze the ability of students to solve the problems of linear motion kinematics expressed in symbolic and numeric representation. Research was survey with cross-sectional design. Research subjects included 26 first year undergraduate students in physics at one of the State Universities in Malang which was consisted of 10 men and 16 women. The research instrument was open-ended test of linear motion kinematics problems expressed in symbolic and numeric representations with a reability of 0,807 The research data were analyzed using descriptive and non-parametric inferential statistics. The results showed that the ability of students to solve linear motion kinematics problems in both symbolic and numeric representation was medium. Students had difficulty solving physical problems in both symbolic and numeric representations. It was also found that the problems of linear motion kinematics in symbolic representations were more difficult for students to solve than numeric representations. The study suggested further research to explore the causes of student difficulties more authentically, e.g. by interviewing or thinking aloud.

A family of novel compliant linear-motion mechanisms based on compliant rolling-contact element pivot

Compliant linear-motion mechanisms are of great use in precision machines, due to their excellent performances such as infinite resolution and low cost. The accuracy of the mechanisms is an important consideration for mechanical design in applications, especially in the case of large working load. Considering that COmpliant Rolling-contact Element (CORE) pivot is characterized with high bearing capacity, the paper adopts it as a building block to design a family of compliant linear-motion mechanisms for applications of heavy load. These mechanisms are achieved by replacing four rigid pivots in a parallel four-bar mechanism with CORE pivots, and the motion accuracy is improved by means of contacting surfaces design of four CORE pivots. Firstly, structures of CORE pivot are introduced and five extended arrangements for bearing heavy load are presented. Meanwhile, motion for the CORE pivot is analyzed and preconditions for achieving a pure roll are discussed. Then, configuration of the compliant linear-motion mechanisms constructed by CORE pivots is obtained, and kinematics of the mechanisms is analyzed and parametric design condition for rectilinear motion is modeled. Based on the condition, detailed topological structures of the mechanisms are designed. Finally, motion simulations and experiment tests are implemented to verify accuracy of the proposed mechanisms. The results demonstrate that the mechanisms proposed in this paper are capable of offering a high-precision linear motion and providing a promising application prospect in precision machines.

Design Issues of a Rotating to Linear Motion Magnetic Converter for Short-Distance Transport Applications

This paper discusses some design issues of a magnetic rotating to linear motion converter (RLMC), suitable for the propulsion system of a short-distance low-capacity vehicle. It basically operates like a magnetic rack, which executes the contactless conversion of the motor torque into a propulsion thrust, deriving from the interaction of on-board permanent magnet (PM) modules and stationary ferromagnetic steel pieces. A design procedure is set up that deals with both the PM module arrangement and the geometric shape of the steel pieces to optimize different performance aspects. A simplified modeling based on 2D transient finite element analyses is carried out to determine the thrust profile and the RLMC losses, which are essential to assess its practical feasibility. Finally, the characteristics as functions of the load angle and speed are determined to enable the prediction of the dynamic power exchange and then of the net energy demand useful to size the on-board source.

New Designs of Magnetic Fluid Seals for Reciprocating Motion

The operating conditions of magnetic fluid seals during reciprocating motion are so different from those observed in rotating motion that the use of their conventional structures for reciprocating motion seals yields no good results. The analysis of the sealing mechanism of magnetic fluid seals in reciprocating motion shows that the operation of these seals is affected by the carry-over phenomenon and magnetic fluid film deformation in the sealing gap, which depends on the velocity of the reciprocating motion. The reduced amount of magnetic fluid in the sealing gap caused by the reciprocating motion of the shaft is the main reason for seal failures. The paper presents a short characterisation of magnetic fluid sealing technology, the principle of sealing, the operation of the magnetic fluid and the seal failure mechanism in linear motion of the shaft. Moreover, some new structural designs of hybrid seals, being combinations of typical hydraulic seals with magnetic fluid seals for reciprocating motion, and some examples of magnetic fluid sealing structures for hydraulic cylinders and piston compressors which have practical application values are presented.

Strategic alterations of posture are delayed in Parkinson’s disease patients during deep brain stimulation

Parkinson’s disease (PD) is characterized by rigidity, akinesia, postural instability and tremor. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) reduces tremor but the effects on postural instability are inconsistent. Another component of postural control is the postural strategy, traditionally referred to as the ankle or hip strategy, which is determined by the coupling between the joint motions of the body. We aimed to determine whether DBS STN and vision (eyes open vs. eyes closed) affect the postural strategy in PD in quiet stance or during balance perturbations. Linear motion was recorded from the knee, hip, shoulder and head in 10 patients with idiopathic PD with DBS STN (after withdrawal of other anti-PD medication), 25 younger adult controls and 17 older adult controls. Correlation analyses were performed on anterior–posterior linear motion data to determine the coupling between the four positions measured. All participants were asked to stand for a 30 s period of quiet stance and a 200 s period of calf vibration. The 200 s vibration period was subdivided into four 50 s periods to study adaptation between the first vibration period (30–80 s) and the last vibration period (180–230 s). Movement was recorded in patients with PD with DBS ON and DBS OFF, and all participants were investigated with eyes closed and eyes open. DBS settings were randomized and double-blindly programmed. Patients with PD had greater coupling of the body compared to old and young controls during balance perturbations (p ≤ 0.046). Controls adopted a strategy with greater flexibility, particularly using the knee as a point of pivot, whereas patients with PD adopted an ankle strategy, i.e., they used the ankle as the point of pivot. There was higher flexibility in patients with PD with DBS ON and eyes open compared to DBS OFF and eyes closed (p ≤ 0.011). During balance perturbations, controls quickly adopted a new strategy that they retained throughout the test, but patients with PD were slower to adapt. Patients with PD further increased the coupling between segmental movement during balance perturbations with DBS ON but retained a high level of coupling with DBS OFF throughout balance perturbations. The ankle strategy during balance perturbations in patients with PD was most evident with DBS OFF and eyes closed. The increased coupling with balance perturbations implies a mechanism to reduce complexity at a cost of exerting more energy. Strategic alterations of posture were altered by DBS in patients with PD and were delayed. Our findings therefore show that DBS does not fully compensate for disease-related effects on posture.

Thermal Correction to the Kinnersley Black Hole in a Lorentz-Violating Dirac Field Theory

According to Lorentz-violating theory, the dynamical equation of Dirac particles in the Kinnersley black hole with variably accelerated linear motion is modified. The Hawking quantum tunneling radiation characteristics of Kinnersley black hole are obtained by solving the modified equation. The expression of the Hawking temperature of Kinnersley black hole has been updated.

PENGARUH PENERAPAN LABORATORIUM VIRTUAL PHET TERHADAP MOTIVASI BELAJAR IPA SISWA PADA MATERI GERAK LURUS

ABSTRAKPenelitian ini bertujuan untuk mengetahui bagaimana pengaruh penerapan laboratorium virtual PhET terhadap motivasi belajar IPA siswa pada materi gerak lurus. Penelitian ini dikategorikan sebagai penelitian eksperimen dengan jenis quasi eksperimen yang menggunakan desain posttest only control group. Populasi dalam penelitian ini adalah seluruh siswa kelas VIII MTs Negeri Ambon tahun ajaran 2020/2021 dengan sampel yaitu kelas VIII4 sebagai kelas eksperimen dan kelas VIII5 sebagai kelas kontrol yang ditentukan dengan teknik sampling yaitu simple random sampling. Instrument yang digunakan dalam penelitian ini adalah kuesioner motivasi belajar IPA siswa yang berisi 46 butir pernyataan (22 butir pernyataan positif dan 24 butir pernyataan negatif). Data hasil pengisian angket motivasi dianalisis dengan uji hipotesis t-test one way menggunakan spss 26. Hasil pengujian hipotesis diperoleh nilai signifikansi sebesar 0,000 < 0,05 yang berarti H0 ditolak dan H1 diterima. Ini menunjukkan bahwa terdapat perbedaan pengaruh yang signifikan motivasi belajar siswa antara siswa yang belajar IPA menggunakan praktikum laboratorium virtual PhET dengan siswa yang belajar IPA secara konvensional. Sehingga dapat disimpulkan bahwa penerapan laboratorium virtual PhET memberikan pengaruh motivasi belajar IPA siswa yang lebih baik pada materi gerak lurus. Kata kunci: Laboratorium virtual; Simulasi PhET; Motivasi belajar; Gerak lurus ABSTRACTThis research aimed to know the effect of using virtual laboratory PhET towards students’ motivation in learning science on linear motion. This research is quasy experimental research that uses posttest only control group design. The population of this research is all grade VIII students of MTs Negeri 1 Ambon in the academic year 2020/2021 and the sample of this research is grade VIII4 as experimental group and VIII5 as control group that determined by simple random sampling technique. The instrument that used to collect the data is questionnaire of students’ motivation in learning science which have 46 items (22 positive questions and 24 negative questions). The data The data were processed in the percentage and analysed by statistical formula of t-test by SPSS 26. The result of t-test shows that Sign. 0000 < 0,05, it mens that there is a significant difference effect of students’ motivation in learning science on the linear motion. Therefore, it can be concluded that implementation of virtual laboratorial PhET has positive effect towards students’ motivation in learning science on the linear motion. Keywords: virtual laboratory; PhET simulation; Motivation in learning; Linear motion