Characterisation of the LMS200 laser beam under the influence of blockage surfaces. Influence on 3D scanning of tree orchards

The geometric characterisation of tree orchards is a high-precision activity comprising the accurate measurement and knowledge of the geometry and structure of the trees. Different types of sensors can be used to perform this characterisation. In this work a terrestrial LIDAR sensor (SICK LMS200) whose emission source was a 905-nm pulsed laser diode was used. Given the known dimensions of the laser beam cross-section (with diameters ranging from 12 mm at the point of emission to 47.2 mm at a distance of 8 m), and the known dimensions of the elements that make up the crops under study (flowers, leaves, fruits, branches, trunks), it was anticipated that, for much of the time, the laser beam would only partially hit a foreground target/object, with the consequent problem of mixed pixels or edge effects. Understanding what happens in such situations was the principal objective of this work. With this in mind, a series of tests were set up to determine the geometry of the emitted beam and to determine the response of the sensor to different beam blockage scenarios. The main conclusions that were drawn from the results obtained were: (i) in a partial beam blockage scenario, the distance value given by the sensor depends more on the blocked radiant power than on the blocked surface area; (ii) there is an area that influences the measurements obtained that is dependent on the percentage of blockage and which ranges from 1.5 to 2.5 m with respect to the foreground target/object. If the laser beam impacts on a second target/object located within this range, this will affect the measurement given by the sensor. To interpret the information obtained from the point clouds provided by the LIDAR sensors, such as the volume occupied and the enclosing area, it is necessary to know the resolution and the process for obtaining this mesh of points and also to be aware of the problem associated with mixed pixels.

Treatment of type B periprosthetic femur fractures with curved non-locking plate with eccentric holes: Retrospective study of 43 patients with minimum 1-year follow-up.

INTRODUCTION: Periprosthetic femur fracture (PFF) is a serious complication after total hip arthroplasty that can be treated using different internal fixation devices. However, the outcomes with curved non-locking plates with eccentric holes in this indication have not been reported previously. The objectives of this study were to determine: (1) the union rate; (2) the complication rate; (3) autonomy in a group of patients with a Vancouver type B PFF who were treated with this plate. HYPOTHESIS: Use of this plate results in a high union rate with minimal mechanical complications. MATERIALS AND METHODS: Forty-three patients with a mean age of 79 years±13 (41-98) who had undergone fixation of Vancouver type B PFF with this plate between 2002 and 2007 were included in the study. The time to union and Parker Mobility Score were evaluated. The revision-free survival (all causes) was calculated using Kaplan-Meier analysis. The average follow-up was 42 months±20 (16-90). RESULTS: Union was obtained in all patients in a mean of 2.4 months±0.6 (2-4). One patient had varus malunion of the femur. The Parker Mobility Score decreased from 5.93±1.94 (2-9) to 4.93±1.8 (1-9) (P=0.01). Two patients required a surgical revision: one for an infection after 4.5 years and one for stem loosening. The survival of the femoral stem 5 years after fracture fixation was 83.3%±12.6%. CONCLUSION: Use of a curved plate with eccentric holes for treating type B PFF led to a high union rate and a low number of fixation-related complications. However, PFF remains a serious complication of hip arthroplasty that is accompanied by high morbidity and mortality rates. LEVEL OF EVIDENCE: Retrospective study, level IV.

Black holes by analytic continuation

In the context of a two-dimensional exactly solvable model, the dynamics of quantum black holes is obtained by analytically continuing the description of the regime where no black hole is formed. The resulting spectrum of outgoing radiation departs from the one predicted by the Hawking model in the region where the outgoing modes arise from the horizon with Planck-order frequencies. This occurs early in the evaporation process, and the resulting physical picture is unconventional. The theory predicts that black holes will only radiate out an energy of Planck mass order, stabilizing after a transitory period. The continuation from a regime without black hole formationaccessible in the 1+1 gravity theory consideredis implicit in an S-matrix approach and suggests in this way a possible solution to the problem of information loss.

Quantum black holes: Nonperturbative corrections and no-veil scenario

A common belief is that further quantum corrections near the singularity of a large black hole should not substantially modify the semiclassical picture of black hole evaporation; in particular, the outgoing spectrum of radiation should be very close to the thermal spectrum predicted by Hawking. In this paper we explore a possible counterexample: in the context of dilaton gravity, we find that nonperturbative quantum corrections which are important in strong-coupling regions may completely alter the semiclassical picture, to the extent that the presumptive spacelike boundary becomes timelike, changing in this way the causal structure of the semiclassical geometry. As a result, only a small fraction of the total energy is radiated outside the fake event horizon; most of the energy comes in fact at later retarded times and there is no problem of information loss. This may constitute a general characteristic of quantum black holes, that is, quantum gravity might be such as to prevent the formation of global event horizons.

Diffraction grating couplers milled in Si3N4 rib waveguides with a focused ion beam

Focused ion beam milling is a processing technology which allows flexible direct writing of nanometer scale features efficiently substituting electron beam lithography. No mask need results in ability for patterns writing even on fragile micromechanical devices. In this work we studied the abilities of the tool for fabrication of diffraction grating couplers in silicon nitride waveguides. The gratings were fabricated on a chip with extra fragile cantilevers of sub micron thickness. Optical characterization of the couplers was done using excitation of the waveguides in visible range by focused Gaussian beams of different waist sizes. Influence of Ga+ implantation on the device performance was studied.

Metallien laserporaus

Lasertarkkuusporauksella on tämän hetken teollisuudessa useita sovelluksia, kuten esimerkiksi mustesuihkukirjoittimet, dieselmoottoreiden polttoainesuuttimet, lääketieteen instrumentit, turbiinien lapojen jäähdytysreiät ja stensiilit. Tässä työssä on tutkittu laserporauksen mahdollisuuksia 99,9 % kupariin sekä EN 1.4301 ruostumattomaan teräkseen (vastaava AISI 304). Ainepaksuuksia oli käytettävissä kolmea: 0,1 mm, 0,5 mm ja 1,0 mm. Vertailun vuoksi valittiin tutkimukseen mukaan ainepaksuudeltaan 1,0 mm EN 1.4432 haponkestävää terästä (vastaava AISI 316L). Tutkimuksessa käytettiin kolmea eritehoista 1,064 µm aallonpituuden Nd:YAG – laseria ja yhtä CO2 – laseria. Poratut reiät kuvattiin elektronimikroskoopilla ja jokaisesta reiästä mitattiin halkaisija, ympyrämäisyys ja kartiokkuus. Lisäksi reiän laatua arvioitaessa tarkasteltiin purseen määrää reikien ympärillä. Tutkimus osoitti, että eri materiaaleihin voidaan porata, laserin säteen laadusta ja aallonpituudesta riippuen, hyvin erikokoisia reikiä. Kartiokkuuteen havaittiin voitavan vaikuttaa polttopisteen paikkaa siirtämällä.

Teräspalkkirakenteiden palomitoitus hiilivetypalossa

Työn tavoitteena oli kehittää teräspalkkirakenteiden palosuunnittelua ja palosuojauksen toteutusta öljynjalostamolla käytettävien kantavien teräspalkkirakenteiden osalta. Lisäksi tavoitteena oli luoda suunnitteluohjeen runko palomitoituksen toteuttamiseksi Neste Engineering Oy:ssä. Ongelmakohtia työssä olivat rakenteiden kapasiteettien tarkka määritys, toimivien toteutusratkaisujen etsiminen, sekä öljynjalostamolla mitoituspalona käytettävän hiilivetypalon SFS-ENV-1992-1-2 käyttö yleisemmin mitoituspalona käytettävän standardipalo ISO-834 sijaan. Työssä perehdyttiin kirjallisuuden perusteella eri palosuojausmenetelmiin. Tarkemman jatkotutkimuksen kohteeksi otettiin jo käytössä hyväksi havaittu teräsputkipalkkien sisäpuoleinen betonitäyttö. Menetelmässä teräsputkipalkin oletetaan kantavan kuormat normaalitilassa ja sisällä olevan raudoitetun betonin palossa. Palkkirakenteiden kapasiteettimitoitus määritettiin laskennallisesti poikkileikkauksille. Mitoitus perustuu palkissa tapahtuvien sisäisten venymien ja puristumien tarkasteluun, sekä poikkileikkauksen tarkan lämpötilajakauman huomioimiseen. Raudoitustankojen ankkurointia palkki-pilari-liitoksessa kehitettiin valmistuksen kannalta yksioikoisemmaksi ja helpommin toteutettavaksi. Palkkien raudoituksiin suunniteltiin kierremuhvijatkoksella toteutettava ankkurointimenetelmä, jolla palkkien raudoitustangot saadaan ankkuroitua täydestä kapasiteetistaan tapauskohtaisesti pilarin vastakkaisella puolella olevaan palkkiin tai ankkurointikappaleella pilariin. Teräsputkipilarin betonivalun vaihtoehtoisiin menetelmiin tutustuttiin. Pilarin alapäähän asennettavan venttiilin läpi tapahtuva täyttö helpottaa betonointityövaihetta. Tutkimuksen tuloksena luotiin suunnitteluohjeen runko, jonka pohjalta voidaan tehdä lopullinen ohje. Myös työn tuloksena saatu laskentaohjelma palkkien momentti-kapasiteetin ja pilarin nurjahduskuorman laskemiseksi helpottaa suunnittelua. Raudoituksen ankkurointiin ja betonointiin esitettyjen menetelmien toimivuus on syytä kokeilla käytännössä ja tehdä jatkokehitys näistä saatavien kokemusten pohjalta.

Changes of Root Length and Root-to-Crown Ratio after Apical Surgery: An Analysis by Using Cone-beam Computed Tomography.

INTRODUCTION: Apical surgery is an important treatment option for teeth with post-treatment periodontitis. Although apical surgery involves root-end resection, no morphometric data are yet available about root-end resection and its impact on the root-to-crown ratio (RCR). The present study assessed the length of apicectomy and calculated the loss of root length and changes of RCR after apical surgery. METHODS: In a prospective clinical study, cone-beam computed tomography scans were taken preoperatively and postoperatively. From these images, the crown and root lengths of 61 roots (54 teeth in 47 patients) were measured before and after apical surgery. Data were collected relative to the cementoenamel junction (CEJ) as well as to the crestal bone level (CBL). One observer took all measurements twice (to calculate the intraobserver variability), and the means were used for further analysis. The following parameters were assessed for all treated teeth as well as for specific tooth groups: length of root-end resection and percentage change of root length, preoperative and postoperative RCRs, and percentage change of RCR after apical surgery. RESULTS: The mean length of root-end resection was 3.58 ± 1.43 mm (relative to the CBL). This amounted to a loss of 33.2% of clinical and 26% of anatomic root length. There was an overall significant difference between the tooth groups (P < .05). There was also a statistically significant difference comparing mandibular and maxillary teeth (P < .05), but not for incisors/canines versus premolars/molars (P = .125). The mean preoperative and postoperative RCRs (relative to CEJ) were 1.83 and 1.35, respectively (P < .001). With regard to the CBL reference, the mean preoperative and postoperative RCRs were 1.08 and 0.71 (CBL), respectively (P < .001). The calculated changes of RCR after apical surgery were 24.8% relative to CEJ and 33.3% relative to CBL (P < .001). Across the different tooth groups, the mean RCR was not significantly different (P = .244 for CEJ and 0.114 for CBL). CONCLUSIONS: This CBCT-based study demonstrated that the RCR is significantly changed after root-end resection in apical surgery irrespective of the clinical (CBL) or anatomic (CEJ) reference levels. The lowest, and thus clinically most critical, postoperative RCR was observed in maxillary incisors. Future clinical studies need to show the impact of resection length and RCR changes on the outcome of apical surgery.

Combined T2 -preparation and two-dimensional pencil-beam inner volume selection.

PURPOSE: To improve coronary magnetic resonance angiography (MRA) by combining a two-dimensional (2D) spatially selective radiofrequency (RF) pulse with a T2 -preparation module ("2D-T2 -Prep"). METHODS: An adiabatic T2 -Prep was modified so that the first and last pulses were of differing spatial selectivity. The first RF pulse was replaced by a 2D pulse, such that a pencil-beam volume is excited. The last RF pulse remains nonselective, thus restoring the T2 -prepared pencil-beam, while tipping the (formerly longitudinal) magnetization outside of the pencil-beam into the transverse plane, where it is then spoiled. Thus, only a cylinder of T2 -prepared tissue remains for imaging. Numerical simulations were followed by phantom validation and in vivo coronary MRA, where the technique was quantitatively evaluated. Reduced field-of-view (rFoV) images were similarly studied. RESULTS: In vivo, full field-of-view 2D-T2 -Prep significantly improved vessel sharpness as compared to conventional T2 -Prep, without adversely affecting signal-to-noise (SNR) or contrast-to-noise ratios (CNR). It also reduced respiratory motion artifacts. In rFoV images, the SNR, CNR, and vessel sharpness decreased, although scan time reduction was 60%. CONCLUSION: When compared with conventional T2 -Prep, the 2D-T2 -Prep improves vessel sharpness and decreases respiratory ghosting while preserving both SNR and CNR. It may also acquire rFoV images for accelerated data acquisition.

The effect on lower spine muscle activation of walking on a narrow beam in virtual reality

To what extent do people behave in immersive virtual environments as they would in similar situations in a physical environment? There are many ways to address this question, ranging from questionnaires, behavioral studies, and the use of physiological measures. Here, we compare the onsets of muscle activity using surface electromyography (EMG) while participants were walking under three different conditions: on a normal floor surface, on a narrow ribbon along the floor, and on a narrow platform raised off the floor. The same situation was rendered in an immersive virtual environment (IVE) Cave-like system, and 12 participants did the three types of walking in a counter-balanced within-groups design. The mean number of EMG activity onsets per unit time followed the same pattern in the virtual environment as in the physical environment-significantly higher for walking on the platform compared to walking on the floor. Even though participants knew that they were in fact really walking at floor level in the virtual environment condition, the visual illusion of walking on a raised platform was sufficient to influence their behavior in a measurable way. This opens up the door for this technique to be used in gait and posture related scenarios including rehabilitation.

Utilização de uma interface do tipo "particle beam" para a obtenção de espectros de massas de compostos pouco voláteis em solução

Due to source contamination and wearing of instrument components problems caused by the direct insertion probe technique, a new way of introduction of low volatile compounds into mass spectrometer was tested. This new scheme comprises the introduction of the low volatile compounds solutions via a six port valve connected to a particle beam interface. Solutions of isatin were injected into this system and the best results were obtained with CH2Cl2, CH3OH and CH3CN. The solution inlet system has shown to be advantageous over the conventional way of direct insertion probe introduction.

Methods to test gas tightness of packages

One of the primary goals for food packages is to protect food against harmful environment, especially oxygen and moisture. The gas transmission rate is the total gas transport through the package, both by permeation through the package material and by leakage through pinholes and cracks. The shelf life of a product can be extended, if the food is stored in a gas tight package. Thus there is a need to test gas tightness of packages. There are several tightness testing methods, and they can be broadly divided into destructive and nondestructive methods. One of the most sensitive methods to detect leaks is by using a non destructive tracer gas technique. Carbon dioxide, helium and hydrogen are the most commonly used tracer gases. Hydrogen is the lightest and the smallest of all gases, which allows it to escape rapidly from the leak areas. The low background concentration of H2 in air (0.5 ppm) enables sensitive leak detection. With a hydrogen leak detector it is also possible to locate leaks. That is not possible with many other tightness testing methods. The experimental work has been focused on investigating the factors which affect the measurement results with the H2leak detector. Also reasons for false results were searched to avoid them in upcoming measurements. From the results of these experiments, the appropriate measurement practice was created in order to have correct and repeatable results. The most important thing for good measurement results is to keep the probe of the detector tightly against the leak. Because of its high diffusion rate, the HZ concentration decreases quickly if holding the probe further away from the leak area and thus the measured H2 leaks would be incorrect and small leaks could be undetected. In the experimental part hydrogen, oxygen and water vapour transmissions through laser beam reference holes (diameters 1 100 μm) were also measured and compared. With the H2 leak detector it was possible to detect even a leakage through 1 μm (diameter) within a few seconds. Water vapour did not penetrate even the largest reference hole (100 μm), even at tropical conditions (38 °C, 90 % RH), whereas some O2 transmission occurred through the reference holes larger than 5 μm. Thus water vapour transmission does not have a significant effect on food deterioration, if the diameter of the leak is less than 100 μm, but small leaks (5 100 μm) are more harmful for the food products, which are sensitive to oxidation.

Improving the oscillating grid method to characterize aquaculture biosolids using a laser beam and image analysis

Quickremovalofbiosolidsinaquaculturefacilities,andspeciallyinrecirculatingaquaculturesystems(RAS),isoneofthemostimportantstepinwastemanagement.Sedimentationdynamicsofbiosolidsinanaquaculturetankwilldeterminetheiraccumulationatthebottomofthetank.

Optical and microstructural properties of MgF2 UV coatings grown by ion beam sputtering process

The optical, mechanical, and microstructural properties of MgF2 single layers grown by ion beam sputtering have been investigated by spectrophotometric measurements, film stress characterization, x-ray photoelectron spectroscopy (XPS), x-ray diffraction, and transmission electron microscopy. The deposition conditions, using fluorine reactive gas or not, have been found to greatly influence the optical absorption and the stress of the films as well as their microstructure. The layers grown with fluorine compensation exhibit a regular columnar microstructure and an UV-optical absorption which can be very low, either as deposited or after thermal annealings at very low temperatures. On the contrary, layers grown without fluorine compensation exhibit a less regular microstructure and a high ultraviolet absorption which is particularly hard to cure. On the basis of calculations, it is shown that F centers are responsible for this absorption, whereas all the films were found to be stoichiometric, in the limit of the XPS sensitivity. On the basis of external data taken from literature, our experimental curves are analyzed, so we propose possible diffusion mechanisms which could explain the behaviors of the coatings.