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Even in a bare classroom, physics can be demonstrated with whatever is there. For example, the optics of the eyes of students can be demonstrated with their own eyes. In this article we demonstrated a lazy eye, depth of field, and the blind spot.

Even in a bare classroom, physics can be demonstrated with whatever is there. For example, the optics of the eyes of students can be demonstrated with their own eyes. In this article we demonstrated a lazy eye, depth of field, and the blind spot.

Classroom demonstrations on eyes and optics with common objects

Classroom demonstrations on eyes and optics with common objects

Infrared Radiation (IR) artwork inspection is typically performed through active thermography and reflectography with different setups and cameras. While Infrared Radiation Reflectography (IRR) is an established technique in the museum field, exploiting mainly the IR-A (0.7–1.4 µm) band to probe for hidden layers and modifications within the paint stratigraphy system, active thermography operating in the IR-C range (3–5 μ m) is less frequently employed with the aim to visualize structural defects and features deeper inside the build-up. In this work, we assess to which extent the less investigated IR-B band (1.5–3 μ m) can combine the information obtained from both setups. The application of IR-B systems is relatively rare as there are only a limited amount of commercial systems available due to the technical complexity of the lens coating. This is mainly added as a so-called broadband option on regular Mid-wave infrared radiation (MWIR) (IR-C’/3–5 μ m) cameras to increase sensitivity for high temperature applications in industry. In particular, four objects were studied in both reflectographic and thermographic mode in the IR-B spectral range and their results benchmarked with IR-A and IR-C images. For multispectral application, a single benchmark is made with macroscopic reflection mode Fourier transform infrared (MA-rFTIR) results. IR-B proved valuable for visualisation of underdrawings, pencil marks, canvas fibres and wooden grain structures and potential pathways for additional applications such as pigment identification in multispectral mode or characterization of the support (panels, canvas) are indicated.

Light beams can carry orbital angular momentum (OAM) associated to the helicity of their phasefronts. These OAM modes can be employed to encode information onto a laser beam for transmitting not only in a fiber link but also in a free-space optical (FSO) one. Regarding this latter scenario, FSO communications are considered as an alternative and promising mean complementing the traditional optical communications in many applications where the use of fiber cable is not justified. This next generation FSO communication systems have attracted much interest recently, and the inclusion of beams carrying OAM modes can be seen as an efficient solution to increase the capacity and the security in the link. In this paper, we discuss an experimental demonstration of a proposal for next generation FSO communication system where a light beam carrying different OAM modes and affected by M turbulence is coupled to the multimode fiber link. In addition, we report a better and more robust behavior of higher order OAM modes when the intermodal dispersion is dominant in the fiber after exceeding its maximum range of operation.

The loss of the quantum phase information in the measurement process constitutes a fundamental limitation to transmission electron microscopy as the electron wave's phase often contains valuable information about the studied specimen. Phase retrieval from focal series is a holographic technique that seeks to recover the lost information from a set of images recorded at different defoci. In spite of its widespread use, especially for wave reconstruction at atomic resolution, a number of fundamental properties (e.g., regarding the conditions for a unique wave function reconstruction) the magnitude of the reconstruction error and the influence of inconsistencies or incomplete data are not well understood. Here, we elaborate on the fundamentals of the technique, making extensive use of the tomographic representation of a focal series as tilt series in phase space. Using this perspective, we discuss, among others, requirements for the focal series for a unique reconstruction, such as the focus interval ranging from the far field at underfocus to the far field at overfocus or the focus step size. We reveal that the prominent Gerchberg–Saxton iterative projection algorithm corresponds to a numerical integration of the quantum Hamilton–Jacobi equation in the small focus step limit. Moreover, we show that the topology of the starting guess divides the solution space of the Gerchberg–Saxton algorithm into equivalence classes, which mitigates the impact of the incompleteness of typical focal series data. To facilitate a focal series reconstruction meeting these theoretical requirements, such as the long range focus interval, we develop a dedicated calibration procedure facilitating the determination of unknown electron optical parameters such as the focal length of the principal imaging lens or the position of object and image planes. The findings are demonstrated with an example of a focal series reconstruction of an electron vortex beam.

Even in a bare classroom, physics can be demonstrated with whatever is there. For example, the optics of the eyes of students can be demonstrated with their own eyes. In this article we demonstrated a lazy eye, depth of field, and the blind spot.

Even in a bare classroom, physics can be demonstrated with whatever is there. For example, the optics of the eyes of students can be demonstrated with their own eyes. In this article we demonstrated a lazy eye, depth of field, and the blind spot.

Classroom demonstrations on eyes and optics with common objects

Classroom demonstrations on eyes and optics with common objects

Growth front scaling aspects are investigated for poly-( p -phenylene–vinylene)-type oligomer thin films vapor-deposited onto silicon substrates at room temperature. For a film thickness d in the range from 15 to 300 nm, commonly used in optoelectronic devices, measurements of the correlation function by atomic force microscopy yields roughness exponents in the range H =0.45±0.04, and an rms roughness amplitude which evolves with film thickness as a power law σ ∝ d β with β =0.28±0.05. The non-Gaussian height distribution and the measured scaling exponents ( H and β ) suggest a roughening mechanism close to that described by the Kardar–Parisi–Zhang scenario which is characteristic of non-surface diffussive growth processes.

An analysis based on crystal symmetry and high-resolution transmission electron microscopy (HRTEM) is presented as a general methodology to identify planar defects on the basal planes of D019 compounds. As a starting point, the possible (close-packing preserving) planar defects are classified in accordance with their visibility, and the magnitude of the displacement vector on prismatic projections. Analysis of experimental HRTEM images, obtained under two different viewing conditions, followed by matching with simulated images, enables unambiguous identification to be made. The methodology is applied to planar defects observed in D019 Co3

This paper concentrates on effects of roughness on the wettability. Surface roughness is described by an rms amplitude Δ, a correlation length ξ, and a roughness exponent H (0 θtr. The transition angle θtr appears to be smaller than 90°, and decreases with increasing roughness exponent H.

Attempts to fabricate mechanical devices on the molecular level1,2 have yielded analogues of rotors3, gears4, switches5, shuttles6,7, turnstiles8 and ratchets9. Molecular motors, however, have not yet been made, even though they are common in biological systems10. Rotary motion as such has been induced in interlocked systems11,12,13 and directly visualized for single molecules14, but the controlled conversion of energy into unidirectional rotary motion has remained difficult to achieve. Here we report repetitive, monodirectional rotation around a central carbon–carbon double bond in a chiral, helical alkene, with each 360° rotation involving four discrete isomerization steps activated by ultraviolet light or a change in the temperature of the system. We find that axial chirality and the presence of two chiral centres are essential for the observed monodirectional behaviour of the molecular motor. Two light-induced cis-trans isomerizations are each associated with a 180° rotation around the carbon–carbon double bond and are each followed by thermally controlled helicity inversions, which effectively block reverse rotation and thus ensure that the four individual steps add up to one full rotation in one direction only. As the energy barriers of the helicity inversion steps can be adjusted by structural modifications, chiral alkenes based on our system may find use as basic components for ‘molecular machinery’ driven by light.

We investigate the electrical transport properties of ITO/conjugated polymer–fullerene/Al solar cells and the role of defect states with the help of admittance spectroscopy and C ( ω )– V measurements in the dark. A characteristic step in the admittance spectrum can be observed in the temperature range 40–320 K, originating from the electrically active defects. The activation energy determined from an Arrhenius plot was found to be 34 meV. The position of the step does not depend on the dc bias voltage which may indicate the pinning of the hole Fermi-level at the interface due to the high density of defect states. The diode capacitance as a function of the reverse bias depends strongly on the device preparation conditions and correlates with the device I – V characteristics. We found a completely bias independent capacitance under reverse bias for the cells with low-power efficiency and almost no rectification under illumination. On the other hand, the high-efficiency cells with good rectification under illumination demonstrate an increase of the capacitance with ac bias even at frequencies above 100 kHz. The former devices are found to be fully depleted, whereas in the latter, a formation of the space charge region can be assumed.

In het dagelijkse leven kom je, misschien zonder er bij stil te staan, voortdurend in contact met toepassingen uit de fotonica. Neem bijvoorbeeld het lezen van dit artikel. Vooraleer dit bij jou terecht is gekomen, heeft het een hele weg afgelegd doorheen het optische vezelnetwerk van het internet. Vervolgens werd het afgedrukt met behulp van laserprinters. Zoniet bekijk je deze tekst op het ingebouwde lcd-scherm van een computer en misschien vind je het zo goed dat je het straks op dvd zal bewaren...

De Wetenschappelijke Scheurkalender biedt 365 intrigerende wetenschappelijke inzichten. Alle disciplines, van de biologie tot de kwantummechanica, komen aan de orde. De bijdragen zijn geschreven door ruim vijftig wetenschappers uit Nederland en Vlaanderen en worden afgewisseld door 52 hilarische cartoons van de Amerikaanse wetenschapscartoonist S. Harris.

To date, the use of liquid crystal grid projection for profilometric applications is gaining in popularity because of its flexibility. Liquid crystal projection devices allow easy adaption of the grid pitch (and thus sensitivity) in for instance Moiré topography, and in-plane translation of the grid position is also readily achieved. However, all methods either use Fourier transform profilometry or digital demodulation in the computer, with the advantage being the measurement speed. The major disadvantage is that the resolution is compromised. Only optical demodulation combined with phase-shifting methods does not yield any resolution. In this paper, we describe a technique which performs this optical demodulation as well as the grid projection with grids on liquid crystal light modulators. This entirely liquid crystal Moiré projection profilometer thus achieves higher resolution, flexibility and ease-of-use than the solely LCD grid projection setups. Theory and application examples are given in this paper, and a study is made of different parameters and algorithms influencing the resolution.

Effect van UV-straling op kleuring van Coleus Blumei 'Wizzard Velvit Red'. Gegevens in bijgaande tabellen: 1) Indeling optische straling; 2) Transmisse voor UV-straling van verschillende dekmaterialen (folie UV, glas UV, glas normaal, folie normaal, folie UV-blok

Nanostripes are observed in melt-textured and single-crystalline samples of the ternary light rare earth (LRE)-compound (Nd 0.33 Eu 0.33 Gd 0.33 )Ba 2 Cu 3 O x (NEG) by means of atomic force microscopy, scanning tunnelling microscopy at ambient conditions, combined with transmission electron microscopy and electron backscatter diffraction. This enables the observation of several important features: The nanostripes are formed by chains of nanoclusters, representing the LRE/Ba substitution. The dimensions of the nanostripes are similar for both types of NEG samples. The periodicity of the nanostripes is found to range between 40 and 60 nm; the shape of the nanoclusters is elliptic with a major axis length between 300 and 500 nm and a minor axis length of about 30–150 nm. The stripes are filling effectively the space in between the twin boundaries. Concerning the flux pinning, the nanoclusters are the important pinning sites, not the nanostripes themselves.

Recent developments of cerium-doped lanthanum-halide scintillators like LaBr3:Ce show a remarkable performance in gamma-ray spectroscopy. When high energy resolution in combination with stopping power is required they provide excellent gamma-ray detector candidates for the use in space missions. Moreover, irradiation tests have shown that such detectors are radiation tolerant. In this paper we discuss a possible application of LaBr in nuclear astrophysics missions. We show results on recent proton irradiation tests at KVI in Groningen (NL) and discuss the damage and activation effects after irradiation. A possible implementation for a focal plane detector in a gamma-ray telescope and the expected performance is presented.

A tooth rheometer designed to investigate the influence of large amplitude oscillatory shear on the macroscopic orientation of complex fluids is described. The rheometer allows in-situ two-directional small-angle scattering measurements, making it possible to observe in particular the orientation process of hierarchically structured block copolymers in dynamics. Experiments performed with a linear poly(vinyl methyl ether) show that, despite a considerable gap/width ratio, the rheometer can be used for adequate rheological measurements. In addition we found an unexpected dependence of the dynamic parameters on the rheometer gap. The small amount of sample required favors the use of this rheometer for measuring the rheological characteristics of new compounds.

A simple and fast, but sensitive TLD method for the measurement of energy and homogeneity of therapeutically used electron beams has been developed and tested. This method is based on the fact that when small thicknesses of high-Z absorbers such as lead are interposed in the high-energy electron beams, the transmitted radiation increases with the energy of the electron beams. Consequently, the ratio of readouts of TLDS held on the two sides of a lead plate varied sharply (by factor of 70) with a change in energy of the electron beam from 5 MeV to 18 MeV, offering a very sensitive method for the measurement of the energy of electron beams. By using the ratio of TL readouts of two types of TLD ribbon with widely different sensitivities, LiF TLD-700 ribbons on the upstream side and highly sensitive CaF2:Dy TLD-200 ribbons on the downstream side, an electron energy discrimination of better than +/- 0.1 MeV could be achieved. The homogeneity of the electron beam energy and the absorbed dose was measured by using a jig in which the TLDS were held in the desired array on both sides of a 4 mm thick lead plate. The method takes minimal beam time and makes it possible to carry out measurements for the audit of the quality of electron beams as well as for intercomparison of beams by mail.

Onderzoek naar de voorspelbaarheid van de vleeskwaliteit van varkenskarkassen heeft aangetoond dat er een relatie bestaat tussen de HGP-meting en de vleeskwaliteit

We investigate roughness effects on electrical conductivity and giant magnetoresistance (GMR) in thin films with self-affine roughness, characterized by the r.m.s. roughness amplitude w , the in-plane correlation length ξ , and the roughness exponent H . It is shown that dynamic roughening (evolution of the roughness parameters) plays an important role in electrical conductivity of growing films, and consequently also in the GMR. In both cases our theoretical predictions are in qualitative agreement with experimental observations.

We present a new method to calculate the scattering of light at the surface of a photonic crystal. The problem is solved in terms of virtual surface-current distributions and the calculation takes full advantage of the existing infinite-space plane-wave expansion method for obtaining the photonic band structure. Working with surface currents makes the calculations less time-consuming by means of reduction of the dimensionality in the problem. The method is tested and illustrated for semi-infinite two-dimensional photonic crystals of small and large dielectric contrast.

A subdivision of space into discrete cells underlies the traditional discrete dipole model. This model presumes that only nonlocal electric interactions between cells govern the electromagnetic response of a condensed matter system. Apart from the case of simple dielectrics, this is not realistic. Cells can also influence each other directly through the wave functions, when those extend across cell boundaries. In general, such nonlocal quantum mechanical interaction requires the use of nonlocal polarizabilities. In this paper it is shown how existing discrete dipole descriptions for clusters, slabs and (semi)-infinite systems have to be altered to incorporate the effects of nonlocal polarizabilities. The modified method is called discrete cellular method.

The paper deals with a discrete dislocation dynamics study of plastic deformation in a thin film caused by thermal mismatch with its substrate. A unit cell analysis is carried out, with dislocations in the film being represented by line singularities in an isotropic linear elastic medium. Their mutual interactions as well as the interactions with the interface and the free surface are accounted for by means of a coupled dislocation dynamics-finite element technique. The formulation includes a set of constitutive rules to model generation, glide, annihilation and pinning of dislocations at point obstacles. The simulation tracks the evolution of the dislocation structure as thermal stress builds up as well as during relaxation under constant temperature, leading to dense dislocation distributions near the interface and a dislocation-free zone along the stress-free surface of the film.

We have studied the influence of electric fields on highly viscous polymer films. An electrohydrodynamic (EHD) instability causes a wave pattern with a characteristic wavelength λ, leading to an array of polymer columns which span the gap of a capacitor device. When represented as a master curve, the data is quantitatively described by an EHD model, without any adjustable parameters. Our results suggest that EHD experiments using polymer films are well suited to study non-equilibrium pattern formation in quasi-two-dimensional systems.

Four versions of low-energy ion scattering (LEIS) measurements are briefly reviewed. In the first version discussed here the charged fraction of scattered noble-gas ions is detected with an electrostatic analyser. The composition of exclusively the outermost layer is probed in this way, even when the surface of the sample is not smooth. The second method probes the surface step density, and thereby growth oscillations, with grazing-angle specular scattering, whereby the scattered particles are measured without energy resolution. An example is given of the observation of oscillations during the growth of Ag on Ag (0 0 1) at several temperatures. The oscillations are compared with oscillations obtained from simulations of the growth process, combined with LEIS simulations. This second method is also sensitive to the structure of the outermost layer. There is no sensitivity to the composition of the surface. In the third method either the beam direction, or the direction of the detector, makes a grazing angle with the surface, and atoms scattered over a large (non-specular) angle are detected with time-of-flight (TOF) resolution. This provides sensitivity only to atoms protruding from the surface, like adatoms, or atoms at step edges. An example is presented whereby this method is used to measure adatom mobilities. Finally the conventional method of measuring with TOF resolution azimuth scans of scattered or recoiled particles in a shadowing or blocking geometry is described. The scans are compared with the results of computer simulations carried out for trial structures. The properties of the program MATCH that can be used efficiently for these simulations are summarised. As an example of the application of this method the determination of the surface structure of Fe 3 O 4 (0 0 1) is presented. The features of the LEIS versions presented are compared with MEIS and HEIS features, with emphasis on the possibility to obtain information on the composition and structure, separately for the first few layers of a sample.

We investigate the influence of the roughness at a nanometre scale on the electrical capacitance of thin films. It is shown that the surface roughness causes an increase of the electrical capacitance depending on the details of the roughness characteristics. For mound rough surfaces, the increase of the electrical capacitance depends strongly on the relative magnitude of the average mound separation λ and the system correlation length ζ. A rather complex behaviour develops for ζ>λ, whereas for ζ

Effect van UV-straling op kleuring van Coleus Blumei 'Wizzard Velvit Red'. Gegevens in bijgaande tabellen: 1) Indeling optische straling; 2) Transmisse voor UV-straling van verschillende dekmaterialen (folie UV, glas UV, glas normaal, folie normaal, folie UV-blok

Effect van UV-straling op kleuring van Coleus Blumei 'Wizzard Velvit Red'. Gegevens in bijgaande tabellen: 1) Indeling optische straling; 2) Transmisse voor UV-straling van verschillende dekmaterialen (folie UV, glas UV, glas normaal, folie normaal, folie UV-blok

Stimulated by a recent paper by Spaepen (Acta mater. 48 (2000) 31) we concentrate on the effect of roughness parameters on stress measurements in thin films for self-affine and mound rough interfaces. A self-affine interface is characterized by a lateral correlation length ξ, an rms roughness amplitude σ, and a roughness exponent H (0

Beschrijving van een methode, ontwikkeld op het laboratorium voor Zuivel en Levensmiddelennatuurkunde van de LU Wageningen in nauwe samenwerking met de TU Delft, waarmee goed en snel de verdeling van de gasfase in de vloeibare fase in de tijd en op verschillende plaatsen in een monster kan worden bepaald. Deze methode is gebaseerd op glasvezeltechniek

The third- and fifth-order Raman response is calculated for vibrational phase relaxation due to stochastic Gaussian frequency fluctuations. This model can be solved exactly using the cumulant expansion technique. It interpolates continuously between the homogeneous and inhomogeneous limit and allows for a description of non-Markovian dynamics arising from finite correlation time(s) of the frequency fluctuations. Model calculations demonstrate that temporally two-dimensional fifth-order Raman experiments are sensitive to the time scale(s) of these frequency fluctuations and also to the life times of the vibrational states. These processes, that cannot be distinguished in nonresonant third-order Raman scattering, can be unequivocally identified in fifth-order experiments.

The order and disorder in quasi-one-dimensional organic conductors is reviewed from a structural point of view. The qualitative features are discussed of the diffuse scattering and of superstructure reflections. The possibilities are considered to obtain structural information from a quantitative analysis of the diffuse scattering. Two examples are presented in detail. For C1TET-TTF(AuI2)0.8 it is shown that the partially ordered AuI2 substructure can be determined from the maxima within the diffuse sheets. For (Perylene)Co(mnt)2, a quantitative description of the first-order satellite reflections requires a saw-tooth shaped modulation function of large amplitude (0.7 A).

Voor controle van de reiniging van apparatuur in de levensmiddelenindustrie is sinds een paar jaar een nieuwe methode beschikbaar: de ATP-bioluminescentiemethode. Het PR heeft samen met het Nederlands Instituut voor Zuivel Onderzoek (NIZO) te Ede gekeken of de methode ook toepasbaar is voor controle van de reiniging van melkwinningsapparatuur. De methode is snel, eenvoudig en objectief, maar het voegt niet veel toe aan zien en voelen.

Voor controle van de reiniging van apparatuur in de levensmiddelenindustrie is sinds een paar jaar een nieuwe methode beschikbaar: de ATP-bioluminescentiemethode. Het PR heeft samen met het Nederlands Instituut voor Zuivel Onderzoek (NIZO) te Ede gekeken of de methode ook toepasbaar is voor controle van de reiniging van melkwinningsapparatuur. De methode is snel, eenvoudig en objectief, maar het voegt niet veel toe aan zien en voelen.

Onderzocht is of de zware metalen cadmium, chroom, koper, nikkel, lood en zink in bodemvochtmonsters met een ICP kunnen worden geanalyseerd. Een conventionele cross-flow-verstuiver verstoof de bodemvochtmatrix zeer goed. De haalbare detectiegrenzen waren echter te laag. Verstuiving van bodemvocht met een ultrasoonverstuiver werd sterk beonvloed door de organische matrix in de monsters. Daardoor worden monsters uit strooisellagen slechter verstoven dan die uit minerale lagen. Filtratie over 0,45 Šm leverde slechter verstuifbare monsters op dan filtratie over 0,025 Šm. De verstuiving is niet verbeterd door de beschreven experimenten. Zware metalen in bodemvocht kunnen in de toekomst worden geanalyseerd met een gevoeliger ICP.

The locally varying strain field in a matrix containing misfitting second phase particles and its effects on diffraction-line broadening have been simulated numerically. A two-dimensional model material has been considered: A matrix with a periodic arrangement of misfitting circular second phase particles. The strain field is calculated numerically from a micro mechanical model that in principle takes into account the elastic interaction of the misfitting particles. Diffraction-line profiles have been calculated as a function of particle fraction and particle/matrix misfit. Shifts and broadenings of these line profiles have been discussed with reference to known characteristics of Eshelby's approach for point imperfections.

Onderzocht is of de zware metalen cadmium, chroom, koper, nikkel, lood en zink in bodemvochtmonsters met een ICP kunnen worden geanalyseerd. Een conventionele cross-flow-verstuiver verstoof de bodemvochtmatrix zeer goed. De haalbare detectiegrenzen waren echter te laag. Verstuiving van bodemvocht met een ultrasoonverstuiver werd sterk beonvloed door de organische matrix in de monsters. Daardoor worden monsters uit strooisellagen slechter verstoven dan die uit minerale lagen. Filtratie over 0,45 Šm leverde slechter verstuifbare monsters op dan filtratie over 0,025 Šm. De verstuiving is niet verbeterd door de beschreven experimenten. Zware metalen in bodemvocht kunnen in de toekomst worden geanalyseerd met een gevoeliger ICP.

Onderzoek naar de voorspelbaarheid van de vleeskwaliteit van varkenskarkassen heeft aangetoond dat er een relatie bestaat tussen de HGP-meting en de vleeskwaliteit

Onderzoek naar de voorspelbaarheid van de vleeskwaliteit van varkenskarkassen heeft aangetoond dat er een relatie bestaat tussen de HGP-meting en de vleeskwaliteit