Helicity Precession of Spin-1/2 Particles in Weak Inertial and Gravitational Fields

We calculate the helicity and chirality effects experienced by a spin-1/2 particle subjected to classical electromagnetic and gravitational fields. The helicity evolution is then determined in the non-relativistic, relativistic, and ultra-relativistic regimes. We find that inertia-gravitation can distinguish between helicity and chirality. Helicity is not conserved, in general, even when the particles are massless. In this case, however, the inertial fields can hardly be applied to the fermions.Comment: 17 pages with no figures. Submitted to Nuclear Physics

Maximal Acceleration Corrections to the Lamb Shift of Muonic Hydrogen

The maximal acceleration corrections to the Lamb shift of muonic hydrogen are calculated by using the relativistic Dirac wave functions. The correction for the $2S-2P$ transition is $\sim 0.38$ meV and is higher than the accuracy of present QED calculations and of the expected accuracy of experiments in preparation.Comment: LaTex file, 9 pages, to be published in Il Nuovo Cimento

Breakdown of Casimir Invariance in Curved Space-Time

It is shown that the commonly accepted definition for the Casimir scalar operators of the Poincare group does not satisfy the properties of Casimir invariance when applied to the non-inertial motion of elementary particles while in the presence of external gravitational and electromagnetic fields, where general curvilinear co-ordinates are used to describe the momentum generators within a Fermi normal co-ordinate framework. Specific expressions of the Casimir scalar properties are presented for spin-1/2 to spin-2 particles inclusive. While the Casimir scalar for linear momentum remains a Lorentz invariant in the absence of external fields, this is no longer true for the spin Casimir scalar. Potential implications are considered for the propagation of photons, gravitons, and gravitinos as described by the spin-3/2 Rarita-Schwinger vector-spinor field. In particular, it is shown that non-inertial motion introduces a frame-based effective mass to the spin interaction, with interesting physical consequences that are explored in detail.Comment: 18 pages, 1 figure; accepted for publication in Annalen der Physi

SISTEM KONTROL INVERTED PENDULUM PADA BALANCING MOBILE ROBOT

ABSTRAK Sistem kontrol merupakan suatu sistem yang menjadi pusat perhatian di bidang robotika. Dimana dengan adanya sistem kontrol ini, robot bisa menjadi lebih cerdas dan canggih. Pada proyek akhir ini akan dibangun sebuah sistem kontrol inverted pendulum pada mobile robot. Inverted pendulum adalah pendulum yang mempunyai titik berat diatas titik tumpunya. Balancing Robot ini selalu menyetimbangkan sistemnya agar pendulum tetap tegak. Sebagai deteksi kemiringan antara robot dengan lantai digunakan sensor Sharp GP2D12. Sensor ini mempunyai output tegangan analog. Data dari sensor ini akan diolah oleh Mikrokontroler ATMega 16. Karena data yang dibawa oleh Sharp GP2D12 ini mempunyai noise, maka data harus difilter. Filter yang dipakai adalah Single Exponential Filter yang bisa mereduksi noise secara optimal disamping juga mempunyai respon waktu yang cepat. Setelah selesai pemrosesan, data diolah dengan menggunakan kontrol PID. Dengan sistem kontrol ini, robot akan bergerak maju mundur searah dengan arah gerak jatuhnya pendulum. Prosentase keberhasilan kontrol PID pada robot ini adalah 90% dengan robot tidak pernah jatuh tetapi berosilasi kecil. Kata Kunci : Inverted Pendulum, Sharp GP2D12, Single Exponential Filter, PID, Balancing Robot

Three-Dimensional (3D) Printed Microneedles for Microencapsulated Cell Extrusion

Cell-hydrogel based therapies offer great promise for wound healing. The specific aim of this study was to assess the viability of human hepatocellular carcinoma (HepG2) cells immobilized in atomized alginate capsules (3.5% (w/v) alginate, d = 225 µm ± 24.5 µm) post-extrusion through a three-dimensional (3D) printed methacrylate-based custom hollow microneedle assembly (circular array of 13 conical frusta) fabricated using stereolithography. With a jetting reliability of 80%, the solvent-sterilized device with a root mean square roughness of 158 nm at the extrusion nozzle tip (d = 325 μm) was operated at a flowrate of 12 mL/min. There was no significant difference between the viability of the sheared and control samples for extrusion times of 2 h (p = 0.14, α = 0.05) and 24 h (p = 0.5, α = 0.05) post-atomization. Factoring the increase in extrusion yield from 21.2% to 56.4% attributed to hydrogel bioerosion quantifiable by a loss in resilience from 5470 (J/m3) to 3250 (J/m3), there was no significant difference in percentage relative payload (p = 0.2628, α = 0.05) when extrusion occurred 24 h (12.2 ± 4.9%) when compared to 2 h (9.9 ± 2.8%) post-atomization. Results from this paper highlight the feasibility of encapsulated cell extrusion, specifically protection from shear, through a hollow microneedle assembly reported for the first time in literature

Reply to Comment on ``Can gravity distinguish between Dirac and Majorana neutrinos?''

This is a reply to a comment (gr-qc/0610098) written by Nieves and Pal about our paper (gr-qc/0605153) published in Phys. Rev. Lett. 97, 041101 (2006).Comment: 1 page, no figures, REVTe