Atmospheric densities and temperatures from the drag analysis of the San Marco Satellite

Atmospheric densities and temperatures from drag analysis of San Marco satellit

Mass Loss Due to Sputtering and Thermal Processes in Meteoroid Ablation

Conventional meteoroid theory assumes that the dominant mode of ablation is by evaporation following intense heating during atmospheric flight. In this paper we consider the question of whether sputtering may provide an alternative disintegration process of some importance.For meteoroids in the mass range from 10^-3 to 10^-13 kg and covering a meteor velocity range from 11 to 71 km/s, we numerically modeled both thermal ablation and sputtering ablation during atmospheric flight. We considered three meteoroid models believed to be representative of asteroidal (3300 kg m^-3 mass density), cometary (1000 kg m^-3) and porous cometary (300 kg m^-3) meteoroid structures. Atmospheric profiles which considered the molecular compositions at different heights were used in the sputtering calculations. We find that while in many cases (particularly at low velocities and for relatively large meteoroid masses) sputtering contributes only a small amount of mass loss during atmospheric flight, in some cases sputtering is very important. For example, a 10^-10 kg porous meteoroid at 40 km/s will lose nearly 51% of its mass by sputtering, while a 10^-13 kg asteroidal meteoroid at 60 km/s will lose nearly 83% of its mass by sputtering. We argue that sputtering may explain the light production observed at very great heights in some Leonid meteors. The impact of this work will be most dramatic for very small meteoroids such as those observed with large aperture radars.Comment: in pdf form, 48 pgs incl figures and table

Meteor masses and luminosity

Analysis of meteor luminous efficiency based on photographic data, taking into account fragmentation effect

Automated Individually-Adaptive Astronaut Training Algorithms in Virtual Reality for Deep Space Missions

Long-duration exploration missions (LDEM) pose a unique challenge for astronaut training. Astronauts may experience a degraded capcity to perform complex tasks due both to the time elapsed from initial ground training and to the neural decrements associated with spaceflight. This effect may be particularly pronounced for complex, mission-critical tasks such as maneuvering spacecraft during entry, descent, and landing (EDL). Since the time delays and crew constraints on deep space missions preclude facilitated, operator-mediated training, mitigating this risk requires a cost-effective, lightweight, and automated system for recurrent training. Virtual reality (VR), long-used as an immersive, easily-programmable, dynamic environment for training, is an ideal medium for training during LDEM. To date, there is no literature investigating the effect of responsiveness, integration, and personalization on the efficacy of automated training algorithms. This study used a virtual simulator to train subjects to pilot and land a spacecraft on the surface of Mars and a physical mock-up of a spacecraft cockpit to put skills acquired during training to the test. The study assessed the effect of multiple training algorithms on skill acquisition, learning retention, progression of training difficulty, subtask performance, and skill transfer between the virtual and physical environments. The training algorithms varied the threshold for difficulty progression (sensitivity), the effect of subtask performance on the difficulty progression of other subtasks (lockstep), and the use of fixed rather than adaptive difficulty progression. The study found that highly responsive training algorithms leads to faster difficulty progressions and higher achieved difficulty in training but lower skill and performance in the cockpit environment. It also found that low levels of subtask integration which allow for discrete rather than unified subtask progressions leads to higher performance and achieved difficulty in training, and slightly better performance outcomes in the cockpit. Finally, the study found that personalized training leads to higher levels of skill and performance in both training and the cockpit compared to non-adaptive, fixed progression training. Future work can build upon these results by analyzing the effect of responsiveness on the duration of the familiarization phase during training as a function of task complexity and expanding analysis on personalization to investigate the limiting effect of fixed training progression on top performing subjects. Future studies should investigate run-dependent shifts in PEST staircases, dynamic variable response paradigms which scale difficulty increments to subject performance, Bayesian methods to predict optimal challenge given both individual and aggregate data, subject-selected difficulty, and the incorporation of unobtrisvely-gathered psychophysiological data to estimate workload and challenge, closing the loop on characterizing and optimizing human performance in space.</p

A Randomized Controlled Clinical Trial on Lithium Disilicate Veneers Manufactured by the CAD–CAM Method: Digital Versus Hybrid Workflow

Pressed lithium disilicate is largely used for veneer manufacturing, but a new block formulation has recently been released on the market. This study evaluated the clinical performance of milled lithium disilicate veneers (LiSi Block, GC Co., Tokyo, Japan) realized with a fully digital or hybrid workflow using modified United States Public Health Service (USPHS) evaluation criteria and survival rates after 24 months of clinical service together with the patient’s satisfaction using the Visual Analog Scale (VAS). A total of 105 veneers on natural anterior teeth were made on twenty-nine patients with LiSi Block (GC, Tokyo, Japan). Patients were randomly divided into three groups: Group 1, 35 veneers realized with a completely digital workflow using Trios 3 (3Shape A/S, Copenhagen, Denmark); Group 2, 35 veneers realized with a completely digital workflow using Experimental IOS (GC, Tokyo, Japan); and Group 3, 35 veneers realized with a hybrid workflow. The restorations were followed up for 24 months, and the modified USPHS evaluation was performed at baseline, 12 months, and 24 months together with periodontal evaluation. Repeated measures two-way ANOVA and the Tukey test were applied to compare the modified USPHS method values (α = 0.05). STATISTICA 10.0 software and SIGMAPLOT 12.0 software were used to perform statistical analysis. There were no statistically significant differences between the three groups and with the interaction of group vs. time periods. The satisfaction scores of 7.35 ± 1.8 and 9.4 ± 0.37 were recorded before and after treatment, respectively. Milled lithium disilicate veneers showed a good clinical outcome after 2 years of clinical service. No difference was found between fully digital or hybrid workflow

Accuracy evaluation of digital impressions on horizontal finish line designs

Aim In the last years, intraoral scanners (IOSs) have gained success in prosthodontics. This study aimed to evaluate the accuracy of digital impressions performed with two different intraoral scanners on subgingival chamfer and shoulder prepared teeth considering all the abutment surface and the marginal level. Material and Methods Two upper arch models were produced with elements #16 and #21 receiving a chamfer and a shoulder preparation design. Each model was scanned 10 times with two IOSs: Medit i700 (Medit Corp, Seongbukgu, South Korea) and TRIOS 3 (3Shape, Copenhagen, Denmark). The trueness on the prepared abutments was measured using Geomagic Control X, by superimposition between the scans performed with the IOSs and the scans performed with a laboratory scanner (Aadva Lab Scan, GC Corporation, Tokyo, Japan), and expressed as RMS deviation values and as a color-coded map. Precision was measured by superimposing the scans of the IOSs showing the highest trueness with the other IOSs' scans. The trueness considering the preparation margin alone was measured as well. Results The IOSs under study demonstrated a high accuracy, with comparable trueness on the prepared abutments and statistically significant differences in precision. Medit i700 demonstrated the highest precision. At the marginal level, statistically significant differences in trueness were observed between the two IOSs with an overall low accuracy. Conclusions Medit i700 and TRIOS 3 provided an acceptable in vitro accuracy in the scanning of abutments with horizontal subgingival preparations, both on incisors and molars. However, none of the scanners used provided an acceptable accuracy when only the margin was evaluated. This suggests an incorrect margin reproduction with a possible alteration in the adaptation of the prosthesis

Analog and digital complete denture bases accuracy and dimensional stability: an in-vitro evaluation at 24 hours and 6 months

Objectives: The study aimed to evaluate the accuracy of 3D printed complete denture bases compared to analog and milling manufacturing. Methods: Denture bases (n = 60) were created using three methods: milling (n = 10), analog (flasking) (n = 10), and 3D printing (n = 40). The 3D printing group was further divided into subgroups and each of the material groups. All samples were scanned, and their surfaces were analyzed using 3D software (Geomagic Control X software, 3D Systems) to compare them to the reference model. The accuracy was assessed using root mean square (RMS) values, reflecting the average deviation between the denture bases and the reference model. Results: At 24 h, the "Temp Print", from 3D printing group had the lowest RMS values (54.20±9.44 μm), indicating higher accuracy, while the "ProBase Hot" from the anlog group showed the highest discrepancies, particularly in the border areas. Over six months, all groups experienced increased RMS values, with the 3d pronted "Denture 3d+" group showing the most significant variations (194.1 ± 49.63 μm). The "Temp Print" group maintained the lowest RMS values, indicating better stability at 6 months. Conclusions: Despite some discrepancies, all denture bases remained within clinically acceptable limits (300 μm). Milled bases were the most stable between 24 h and six months. In terms of accuracy and stability, 3D printed resins are suitable for both prototypes and definitive dentures. Further research is required to confirm the clinical acceptability of these materials. Clinical significance: Accuracy in the fabrication of denture bases is paramount for ensuring proper fit, function, and comfort for patients. Analog, addictive and subtractive manufacturing methods of production obtained good dentures accuracy

Outcomes evaluation of a patient treated with roots immediate digital denture: Patient evaluation after full digital dentures

The immediate dentures fabrication in the analogic manner may be an hight timeconsuming and unreliable procedure. The purposes of this article were both to describe a simplified protocol based on a digital workflow used to fabricate a set of immediate dentures and to report patient functional and quality of life data. The digital intraoral scans were recorded and used for dentures design, the teeth arrangement proposed by the software was superimposed to patient frontal photo in order to simulate the aesthetic proposal. The resulted Standard Tessellation Language files were exported to a milling machine for denture fabrication. After immediate denture delivery the remaining lower canine roots were used to retain the prosthesis. In order to evaluate the different effects of the treatment on masticatory efficiency, bite force and health- related quality of life (OHRQoL) data were measured before and after treatment. The patient reported a good adaptation form the delivery, an improvement for all the aspects evaluated after prostheses roots anchorage

Comparison of marginal fit and sealing ability of luted lithium disilicate crowns fabricated with CAD/CAM technology using two different intraoral scanners

Aim The aim of this in vitro study was to compare marginal fit discrepancy of lithium disilicate single crowns fabricated with computer-aided design and computer-aided manufacturing (CAD/CAM) technology using two digital impression systems. Materials and methods 20 molars were prepared for the placement of lithium disilicate single crowns with vertical margins. Teeth were scanned using a model scanner, in order to create master scans. Then two intraoral scanners (IOS) were used to take impressions of all the 20 prepared teeth: Trios (3 Shape, Copenhagen, Denmark) and Aadva (GC, Tokyo, Japan), so that abutments were scanned with both devices. Then 40 lithium disilicate crowns were fabricated with CAD/CAM technology: each abutment had two crowns made with the two IOS. Then, 20 crowns (10 randomly selected from each IOS group) were luted to the 20 prepared teeth. The crowns were tested for marginal leakage by means of aluminum nitrate solution. Then, teeth were embedded in self-curing transparent resin and cut into 1 mm thick slices by means of a low speed, precision cutting machine (Buehler Isomet) using a diamond blade. The slices of each tooth were observed under optical microscope to evaluate the amount of leakage, if any. Then, the slices were sputter coated with gold and observed under scanning electron microscope (SEM) to evaluate the thickness of the cement at the margins. Results No statistically significant differences were found, neither regarding the nanoleakage of the crowns made with the two tested IOS nor regarding cement thickness. Measurements of cement thickness were on average within the acceptable limits considered. Conclusions Both IOS tested showed good performances and, from the results of this in vitro study, can be considered useful for clinical application

Microleakage of three different combinations of adhesive and composite resins

Aims The aim of the present in vitro study was to evaluate the influence of 3 adhesive systems on microleakage of direct composite restorations with proximal margins under the cement-enamel junction (CEJ) and in the enamel. Materials and methods In 30 extracted molars standardized MOD (mesio-occlusal-distal) cavities were prepared with a proximal margin located 1 mm under the cement-enamel junction and another one in the enamel, and subsequently randomly divided in 3 groups of 10 using 3 different adhesives and the same composite: Flowable (G-aenial Universal Injectable, GC) + universal adhesive (G2-Bond Universal, GC) with selective-etch technique (Group 1); Flowable (G-aenial Universal Injectable, GC) + self-etch adhesive (Clearfil SE Bond 2, Kuraray) with 2-step technique (Group 2); Flowable (G-aenial Universal Injectable, GC) + total-etch adhesive (Optibond FL, Kerr) with 3-step technique (Group 3). Samples were tested for microleakage using silver nitrate and infiltration was classified in 5 levels. The differences in microleakage were statistically evaluated with significance set at p&lt;0.05. Results In the margin located in the enamel, group 1 showed an average of 0 microleakage, group 2 an average of 0.2 and group 3 an average of 0.1. In the margin located in the dentin, group 1 showed an average score of 1.1, group 2 of 2.15 and group 3 of 1.25. No statistically significant difference was found in the enamel. Conclusion The combination of adhesive G2-Bond Universal and Optibond FL showed the highest sealing ability both in margins located in the enamel and margins located in the dentin. The adhesive interface in the enamel produced a very good seal, while the adhesive interface in the dentin showed varying degrees of microleakage in all groups