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In order to obtain a widespread application of Additive Manufactured (AM) technology in the aircraft industry for fatigue critical parts, a detailed characterization of the Fatigue and Damage Tolerance (F&DT) behavior of structural components is required. Metal AM techniques in particular are prone to internal defects inherently present due to the nature of the process, which have a detrimental effect on fatigue properties. In the present work, Ti6Al4V and Inconel 718 coupons with artificially induced defects of different dimensions were produced by the Laser Powder Bed Fusion (LPBF) technique. Fatigue tests were performed, and a different defect sensitiveness was observed between the two materials with Inconel being more defect tolerant compared to Titanium. The environmental role at the crack tip of internal defects was discussed, and based on a purely fracture mechanics approach, a simplified stress–life–defect size model was finally devised. The experimental test results together with the information obtained from the fracture surface analysis of tested samples are used to validate the model predictions. The proposed approach could be adopted to define a critical defect size map to be used for tailored Non-Destructive Testing (NDT) evaluation.

In order to obtain a widespread application of Additive Manufactured (AM) technology in the aircraft industry for fatigue critical parts, a detailed characterization of the Fatigue and Damage Tolerance (FDT) behavior of structural components is required. Metal AM techniques in particular are prone to internal defects inherently present due to the nature of the process, which have a detrimental effect on fatigue properties. In the present work, Ti6Al4V and Inconel 718 coupons with artificially induced defects of different dimensions were produced by the Laser Powder Bed Fusion (LPBF) technique. Fatigue tests were performed, and a different defect sensitiveness was observed between the two materials with Inconel being more defect tolerant compared to Titanium. The environmental role at the crack tip of internal defects was discussed, and based on a purely fracture mechanics approach, a simplified stress-life-defect size model was finally devised. The experimental test results together with the information obtained from the fracture surface analysis of tested samples are used to validate the model predictions. The proposed approach could be adopted to define a critical defect size map to be used for tailored Non-Destructive Testing (NDT) evaluation.

International audience; The aircraft industry is always looking for improved efficiency through higher in-service engine temperatures and lighter structures. Titanium-based alloys are good candidates for such applications because of their high specific strength. However, when exposed to high-temperature oxidizing environments, a large amount of dissolved oxygen can be found in such alloys beneath the growing oxide scale, possibly leading to embrittlement. Consequently, evaluating the oxidation resistance of these alloys is essential. With this aim, long-term oxidation tests were carried out on Ti6242S alloy between 500 and 650 °C to study the effect of temperature, surface preparation and microstructure on oxide scale and oxygen dissolution. While increasing the temperature from 560 to 625 °C led to accelerated oxidation kinetics, surface preparation had no noticeable effect on mass variations and oxygen diffusion profiles. Regarding microstructure, when comparing Ti6242S samples having similar α-phase fraction but very different microstructures (fineness and morphology), there wasn’t any significant effect found on mass change and oxygen diffusion after 1 kh at 650 °C.

Electron Beam Additive Manufacturing (EBAM) is a Wire Directed Energy Deposition (W-DED) process that is receiving much more attention than other Additive Manufacturing (AM) techniques, especially in the aeronautical sector for the serial production of metallic parts. However, this technique leads to singular microstructures due to the rapid heating and cooling cycles generated during the deposition of the pieces. In this work, a first identification of the main microstructural features of Ti-6Al-4V parts manufactured by EBAM technology is performed to better understand the general characteristics of this type of parts for further improvement of this technology. The characterization is carried out by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM) observations, and Energy Dispersive X-Ray Spectrometry (EDS) analysis. The most remarkable aspects found are the formation of long columnar prior beta grains throughout several layers in the built material and the presence of many parallel thermal bands perpendicular to the thermal gradient. Quantitative measurements such as the average width of the α lamellae, the volume fraction of β phase, and the chemical composition at different positions are also accomplished. A heterogeneous microstructure is reported, which mainly derives from the complex and diverse thermal histories at the different positions of the deposited material. In addition, Al vaporisation is noticed. However, no significant change along the deposit material is observed for a same configuration. Next, experiments will focus on the influence of different key processing parameters on the microstructure and mechanical properties.

Les phototraumatismes oculaires sont des lesions traumatiques d´origine photochimique. Elles sont responsables de lesions retiniennes ou maculaires qui peuvent etre graves et irreversibles. Nous rapportons le cas d´un patient de 35 ans de sexe masculin, sans antecedent particulier, recu pour une baisse de l´acuite visuelle de survenue brutale aux deux yeux a la suite de l´observation du soleil lors d´une seance de priere appele « danse du soleil ». L´effet deletere des rayons solaires sur les structures du globe oculaire a ete decrit depuis l´antiquite. L´avenement de la tomographie en coherence optique (OCT) a permis une meilleure approche des lesions maculaires solaires. Les phototraumatismes sont des lesions de gravite diverses qui generalement sont evitables par la sensibilisation.

Objective: Cataract is a partial or total opacification of the lens responsible for blindness. The treatment is surgical. The purpose of our study was to evaluate the results of the newly introduced manual small incision cataract surgery (SICS) and compare them with those of the conventional extra-capsular extraction method. Patients and Method: Analytical cross-sectional study was carried out at the ophthalmology department of the University Hospital of Bouake for a period of 1 year. Results: The two surgical techniques were compared at equal proportions. The average duration of interventions was longer during the sutured Extra Capsular Extraction (ECE) compared to the SICS. Rupture of the posterior capsule with vitreous exit, which was the most observed intraoperative complication, was predominant with ECE with suture (16%) against 8% for SICS. Corneal edema observed in the early postoperative period, was predominant with sutured ECE (30%), against 20% for SICS. Corneal edema, which was more observed with EEC compared to SICS, dominated secondary and late postoperative complications. Post-operative astigmatism induced by ECE with suture was between ?2 and ?4 dioptre in 51.5% of patients and between ?0.5 and ?2 dioptre in 73.91% of SICS. Visual acuity without correction in the early days was better with SICS. Conclusion: In this comparative study of cataract surgery, we noted superimposable results for both techniques. However, the prevalence of pre- and post-operative complications was more frequent with sutured ECE. The technique without suture allows visual recovery and a quick return to normal life.

Objective: To describe the epidemiological profile and indications of mutilating eyeball surgery in Abidjan. Patients and methods: This is a retrospective descriptive study on the files of eviscerated, enucleated or exentered patients in the Ophthalmology Department of the University Hospital of Yopougon from January 2010 to December 2016. The parameters studied were: socio-demographic characteristics, indications of mutilating surgery, anesthetic technique, operative technique and patient evolution. Results: During the study period, 59 patients underwent surgery for mutilating eye surgery out of a total of 11,114 procedures, a frequency of 0.53%. The average age of the patients was 31 years with extremes of 3 years and 67 years. Men predominated in 62.1% of cases with a sex ratio of 1.64. Patients came from rural areas in 68.5% of cases. The main indications of the mutilating surgery were: post-inflammatory phthisis (58.6%) and tumoral affections (29.31%). Evisceration was the most common operative technique (67.2%). In 68% of cases the interventions were performed under peribulbar anesthesia. Patients with evisceration (67.2%) and enucleation (5.1%) all benefited from prosthetic equipment. Conclusion: The mutilating surgery of the eyeball is responsible for serious psychological and sociological impacts. The seriousness of these repercussions requires primary prevention through early and adequate management of eye conditions.

Aircraft industry always looks for higher in-service temperatures and lighter structures. With a high specific strength, Ti-based alloys are good candidates for such applications. However, when exposed to oxidizing environments at high temperatures, they undergo large oxygen dissolution while forming an oxide scale, which can greatly affect their mechanical properties. Then, evaluating the oxidation resistance and mechanical behavior of such alloys is essential. In this aim, long term oxidation tests were performed under laboratory air between 500 °C and 625 °C on two Ti-based alloys: β21s, exhibiting a fully β microstructure supposed to dissolve lower amount of oxygen and nitrogen, and Ti6242S, with an α/β microstructure. The oxidized samples were characterized using XRD, Raman spectroscopy, SEM-EDS and micro-durometer. As for the mechanical behavior, tensile tests were performed at room temperature on not aged and on oxidized samples. While larger mass variations were obtained at 500 and 560 °C and up to 997 h at 625 °C for β21s, its mass variations became lower than those of Ti6242S for longer durations at 625 °C. Nevertheless, β21s exhibited thicker micro-hardness affected depths and underwent larger mechanical property modifications compared to Ti6242S.

Additive Manufacturing (AM) is rapidly expanding in aviation due to the advantages it offers compared to conventional manufacturing routes. It allows the production of geometry optimized complex parts with an efficient use of material. However, in order to design reliable parts using this novel manufacturing route, the changes it involves in material properties, defects and shape of parts need to be understood. This paper presents an industrial structural analysis approach applied by AIRBUS to justify newly introduced AM parts on aircraft. Some areas for future development and improvement are also presented.

International audience; Intradermal (ID) vaccination constitutes a promising approach to induce anti-infectious immunity. This route of immunization has mostly been studied with influenza split-virion vaccines. However, the efficacy of ID vaccination for sub-unit vaccines in relation to underlying skin innate immunity remains to be explored for wider application in humans. Relevant animal models that more closely mimic human skin immunity than the widely used mouse models are therefore necessary. Here, we show in domestic swine, which shares striking anatomic and functional properties with human skin, that a single ID delivery of pseudorabies virus (PRV) glycoproteins without added adjuvant is sufficient to trigger adaptive cellular and humoral immune responses, and to confer protection from a lethal respiratory infection with PRV. Analysis of early events at the skin injection site revealed up-regulation of pro-inflammatory cytokine and chemokine genes, recruitment of neutrophils and monocytes and accumulation of inflammatory DC. We further show that the sustained induction of pro-inflammatory cytokine genes results from the combined effects of skin puncture, liquid injection in the dermis and viral antigens. These data highlight that immune protection against respiratory infection can be induced by ID vaccination with a subunit vaccine and reveal that adjuvant requirements are circumvented by the mechanical and antigenic stress caused by ID injection, which triggers innate immunity and mobilization of inflammatory DC at the immunization site. ID vaccination with sub-unit vaccines may thus represent a safe and efficient solution for protection against respiratory infections in swine and possibly also in humans, given the similarity of skin structure and function in both species.

International audience; Titanium-based alloys are increasingly used in aircraft industry due to their good mechanical properties and low density. To reach better efficiencies, the engine design is constantly evolving and the temperature of the combustion chamber is always increasing. Then, surrounding parts are exposed to higher working temperatures and consequently have to cope with more severe oxidation phenomena. For Ti-based alloys, this leads to the formation of an external oxide scale and a large oxygen dissolution in the metal, which may be detrimental for ductility. As nitrogen is the major element of the atmosphere, it seems relevant to study its effect on the oxidation behavior of Ti-6Al-2Sn-4Zr-2Mo-0.1Si titaniumbased alloy used for these applications. Thermogravimetric analyses were carried out at 650 °C for 100 h in synthetic air (20%O2–80%N2) and in a mixture of 20%O2–80%Ar. Results showed that nitrogen decreases the oxidation kinetics by slowing down the oxide scale growth but also by limiting the oxygen dissolution inthe alloy.

At high temperatures under oxidizing environments, titanium-based alloys form an oxide scale and dissolve large amount of oxygen in their metallic matrix. Oxygen dissolution is a cause of embrittlement. Nitrogen is a secondary oxidant, which also dissolves in titanium during oxidation in air. Oxidation experiments of Ti-6Al-2Sn-4Zr-2Mo-0.1Si titanium-based alloy at 650 °C for 1000 h in synthetic air (20%O2- 80%N2) and in a mixture of 20%O2-80%Ar, showed that nitrogen reduces both oxide scale growth and oxygen dissolution. Atom probe tomography revealed that nitrogen effect is due to the formation of an interfacial layer of nitride Ti2N but also to the formation of a nitrogen rich a-Ti-based solid solution, which both act as difiusion barriers for oxygen because of their low oxygen solubility.

Whereas the knowledge of skin thickness is essential to determine microneedle length and ensure proper administration of and better responses to intradermal vaccines, very few figures are available, especially in infants and children. Using ultrasound echography, we investigated skin thickness in 384 children aged 4-7, 12-18, and 54-66 months at potential body sites for intradermal vaccine delivery: deltoid, suprascapular, upper back, and lumbar area. The mean epidermis plus dermis thickness was significantly higher at the suprascapular than at the deltoid site (1.29mm vs. 1.22mm) and remained relatively unchanged whatever the BMI, age, sex, and skin phototype. In the 43 children aged 54-66 months, the mean skin thickness was significantly higher in the upper than in the lumbar area (1.39mm vs. 1.31mm). In this study setting, the heterogeneity in skin thickness cannot be considered sufficient to indicate various microneedle lengths for various ages or injection sites.

The advantages of intradermal (ID) vaccine administration have been well documented but difficulties in performing ID vaccination using existing techniques and equipment have limited it's clinical application. In the present study, a new ID injection technique and associated microinjection system is described and evaluated in a swine and Human models. Clinical investigation models included: injection site imaging (X-ray and 3D ultrasound echography), histological examination of injection sites, fluid injection volume accuracy measurement, subject' perceived pain and local skin reactivity were specifically developed. These evaluations showed that microinjection system can make the practice of ID vaccination easy to perform, reliable and safe, thus setting the stage for broader clinical application of ID vaccine delivery.

Colloque avec actes et comité de lecture. Internationale.; International audience; Les alliages de titane sont utilisés dans les composants aéronautiques tels que les structures secondaires de fixation du moteur. Augmenter l''efficacité du moteur conduit à une augmentation de la température de ces composants. Pour améliorer l'évaluation de la durée de vie de ces pièces, il est nécessaire d'obtenir une meilleure compréhension des changements en service, dans le comportement mécanique. Ceux-ci sont dus à l'enrichissement en oxygène de l'alliage pendant son oxydation. Dans ce travail, des échantillons minces en alliage Ti-6Al-2Sn-4Zr-2Mo-0.1Si ont été pré-oxydés pendant des durées contrôlées afin d'obtenir différentes épaisseurs de la couche affectée par l'oxygène. L'analyse par résonance acoustique permet d'obtenir le module de Young à différentes températures, des essais de traction et de fluage sont ensuite réalisés. En utilisant des échantillons minces, l'effet de la zone de diffusion de l'oxygène (ODZ) sur les propriétés mécaniques a été déterminé.

Intanza® 9 μg (Sanofi Pasteur), a trivalent split-virion vaccine administered by intradermal (ID) injection, was approved in Europe in 2009 for the prevention of seasonal influenza in adults 18 to 59 years. Here, we examined the immune responses induced in adults by the ID 9 μg vaccine and the standard trivalent intramuscular (IM) vaccine (Vaxigrip® 15 μg, Sanofi Pasteur). This trial was a randomized, controlled, single-center, open-label study in healthy adults 18 to 40 years of age during the 2007/8 influenza season. Subjects received a single vaccination with the ID 9 μg (n = 38) or IM 15 μg (n = 42) vaccine. Serum, saliva, and peripheral blood mononuclear cells were collected up to 180 days post-vaccination. Geometric mean hemagglutination inhibition titers, seroprotection rates, seroconversion rates, and pre-vaccination-to-post-vaccination ratios of geometric mean hemagglutination inhibition titers did not differ between the two vaccines. Compared with pre-vaccination, the vaccines induced similar increases in vaccine-specific circulating B cells at day 7 but did not induce significant increases in vaccine-specific memory B cells at day 180. Cell-mediated immunity to all three vaccine strains, measured in peripheral blood mononuclear cells, was high at baseline and not increased by either vaccine. Neither vaccine induced a mucosal immune response. These results show that the humoral and cellular immune responses to the ID 9 μg vaccine are similar to those to the standard IM 15 μg vaccine.

Background. Porcine skin is increasingly being employed as a model of human skin in various research fields, including pharmacology, toxicology and immunology, with particular interest in percutaneous permeation and organ transplantation. Porcine skin shows several anatomical and physiological similarities, but also some differences, with human skin, but few in depth comparative studies are so far available. Ojectives. To study the immunohistochemical properties of normal porcine skin in comparison with human skin. Materials and methods. We performed a histological and immunohistochemical study on frozen and formalin-fixed, paraffin-embedded skin biopsies from domestic swine and normal human skin, using a panel of 93 monoclonal or polyclonal antibodies recognizing various human and porcine skin cell types or structures. Results. We found that several antibodies used to detect normal human skin cells showed equivalent immunoreactivity on normal porcine skin. However, some antibodies commonly used to detect human skin antigens remained unreactive on porcine skin. Conclusions. Our findings highlight the main immunohistochemical properties of porcine skin in comparison with those of human skin and provide a morphological and immunohistochemical basis useful to researchers using porcine skin.

Cecile Berteau1, Florence Schwarzenbach1, Yves Donazzolo2, Mathilde Latreille2, Julie Berube3, Herve Abry1, Joël Cotten1, Celine Feger1, Philippe E Laurent11BD Medical Pharmaceutical Systems, Le-Pont-de-Claix, 2Eurofins Optimed Clinical Research, Gières, France; 3Statistics, BD Corporate, Franklin Lakes, NJ, USAObjective: A disposable autoinjector was developed for subcutaneous (SC) self-injection by patients with chronic diseases. To verify its performance and evaluate its acceptance, a clinical study was conducted in healthy volunteers, comparing SC injections performed by subjects using the autoinjector with SC injections performed by nurses using a syringe.Methods: This was a randomized, single-center, crossover study comparing SC self-injection using an autoinjector with SC nurse-administered injection using a syringe. Two volumes (0.2 mL and 1 mL) were injected into healthy volunteers. Study objectives included assessment of the accuracy and consistency of the volume injected by the injection systems, and skin reaction and pain associated with the injection. The fluid depot in the SC tissue layer was evaluated by ultrasound. Subject acceptance was evaluated using questionnaires on attitudes and emotions towards the injection technique, and challenged by seeking the subjects’ preferred system for a final study injection or future treatment.Results: A total of 960 injections (480 with autoinjector, 480 with syringe) were performed in 40 subjects. There were no significant differences in mean fluid leakage and injected volumes between the systems. Pain associated with the injection was significantly lower with the autoinjector than with the syringe. Local skin reaction at the injection site was overall satisfactory. Injections were appropriately performed by all subjects. At study end, all 40 subjects preferred the autoinjector for a final study injection and for future treatment.Conclusion: This study indicated that the autoinjector used by the subject was similar to a syringe used by a nurse in terms of performance and safety in administering the injections, and better in terms of pain, overall acceptance, and preference.Keywords: subcutaneous injection, autoinjector, self-injection, injection pain, preference, acceptance

International audience; In the present pilot study, intradermal ID delivery systems with a BD microneedle from 1 to 3mm in length, and epidermal delivery (BD skin abrader) through abraded skin surface relative to standard intramuscular injection were evaluated. Circulating neutralizing antibodies were measured against the rabies virus after the Vero cells rabies vaccine was administered at D0, D7, D21 and D49. This clinical evaluation in 66 healthy volunteers shows that ID delivery using BD microneedle technology of 1/4 the IM antigen dose is safe, efficient and reliable, resulting in a protective seroconversion rate. In contrast, the epidermal delivery route did not produce an immune response against the rabies vaccine.

Seasonal influenza epidemics are associated with high morbidity and mortality particularly in high-risk patients. Conventionally administered influenza vaccines show reduced efficacy in populations with weakened immune systems such as solid-organ transplant patients. This study assesses the safety and immunogenicity of an intradermally administered influenza vaccine in renal transplant patients previously identified as non-responders to a licensed trivalent inactivated influenza vaccine (TIV). Renal transplant patients with low or no hemagglutination inhibiting (HI) antibody response to an A influenza (H3N2) vaccine strain were enrolled in a descriptive phase II, open-label, randomized, multicentre trial: 31 received an investigational intradermal TIV, and 31 received a conventionally administered TIV. Both vaccines contained 15 μg hemagglutinin (HA) per strain. The 62 study subjects were selected from 201 renal transplant patients aged 18-60 years who had been vaccinated in the previous year with a conventionally administered TIV. Vaccination was safe and well tolerated by each administration route. The immunogenicity results of this descriptive study showed ID TIV vaccination to induce HI antibody responses that trended higher in renal transplant patients than conventionally administered TIV. Our results suggest that ID influenza vaccination may offer enhanced immunogenicity and protection in persons who do not respond well to conventional TIV. Further studies should be conducted in immunocompromised populations to validate the trends for higher efficacy of ID vs. conventional route of immunization against influenza.

The skin has long been recognized as an attractive target for vaccine administration. A number of clinical studies have tested the epidermal and dermal routes of delivery using a variety of vaccines over the years. In many cases, cutaneous administration has been associated with immunological benefits, such as the induction of greater immune responses compared with those elicited by conventional routes of delivery. Furthermore, there is a growing body of evidence to suggest that such benefits may be particularly important for certain higher-risk populations, such as the elderly, the immunocompromised and cancer patients. Despite the potential advantages of vaccination via the skin, results have sometimes been conflicting and the full benefits of this approach have not been fully realized, partly due to the lack of delivery devices that accurately and reproducibly administer vaccines to the skin. The 5-year outlook, however, appears quite promising as new cutaneous delivery systems advance through clinical trials and become available for more widespread clinical and commercial use.

Background To reduce injection pain and improve satisfaction, a thinner (29-gauge [29G]), sharper (5-bevel) needle than the 27G/3-bevel needle used previously to inject interferon (IFN) beta-1a, 44 or 22 mcg subcutaneously (sc) three times weekly (tiw), was developed for use in multiple sclerosis (MS). Methods Two clinical trials in healthy volunteers and five surveys of patients with MS were conducted to assess whether the 29G/5-bevel needle with a Thermo Plastic Elastomer (TPE) needle shield (a sleeve that houses the tip of the needle in a secure location) is an improvement over the 27G/3-bevel needle with a rubber shield for injection of IFN beta-1a, 44 or 22 mcg sc tiw. Parameters assessed were: pain and ease of insertion (healthy volunteer and nurse responses on subjective pain measurement scales); and patient satisfaction (surveys of patients with MS). Results In healthy volunteers, the 29G/5-bevel needle with TPE shield was associated with the least perceived pain on the Visual Analog Scale (VAS) and Verbal VAS (VB-VAS); mean VAS pain scores decreased by 40% and skin penetration improved by 69% compared with the 27G/3-bevel needle with standard rubber shield (p < 0.01). Pooled results from surveys of patients with MS indicated that 63% of patients thought that injections were less painful with the 29G/5-bevel needle than the 27G/3-bevel needle. Results from individual surveys indicated that the 29G/5-bevel needle was an improvement over the 27G/3-bevel needle for ease of insertion, injection-site reactions, bruising, burning and stinging. Conclusion Together these studies indicate that the 29G/5-bevel needle with the TPE shield is an improvement over the 27G/3-bevel needle with standard rubber shield in terms of pain, ease of insertion and patient satisfaction. These improvements are expected to result in improved compliance in patients with MS treated with IFN beta-1a, 44 or 22 mcg sc tiw.

There has been a recent resurgence of interest in intradermal vaccine delivery. The physiological advantages of intradermal vaccine delivery have been known for some time, but the difficulties associated with performing an intradermal injection have historically limited its use. New delivery systems currently in development facilitate convenient intradermal vaccination, unlocking the potential advantages of this delivery route, and potentially transforming vaccine delivery.

Florence Schwarzenbach,1 Michèle Dao Trong,1 Laurent Grange,2 Philippe E Laurent,3 Herve Abry,4 Joël Cotten,5 Corinne Granger1 1Medical Affairs, Becton Dickinson Medical Pharmaceutical Systems, Le-Pont-de-Claix, France; 2Rheumatology Clinic, South University Hospital, Echirolles, France; 3Creabio-ra SAS, Centre Hospitalier, Givors, France; 4Commercial Development Self Administration/Injectable Systems, Becton Dickinson Medical Pharmaceutical Systems, Le-Pont-de-Claix, France; 5Marketing, Becton Dickinson Medical Pharmaceutical Systems, Le-Pont-de-Claix, France Purpose: This study evaluated the human factors affecting the ease of use of a disposable autoinjector developed for subcutaneous self-injections performed by patients with chronic diseases. Materials and methods: This was a randomized, single-center study conducted with 65 patients with rheumatoid arthritis. Patients performed six simulated injections. Assessments of patient device acceptance and device usability were made by patient reports and independent observations of compliance with the device instruction for use (IFU) following single injections and repeated injections. Results: A total of 390 simulated injections were performed. Patient device acceptance was high; more than 90% of patients found each of the tested criteria to be acceptable (>80% was required for statistical significance; P

The objective of this thesis is to gain a better understanding of the process by which residential land prices are determined and change over time. A special concern is also shown for the causal relationship between the prices of building lots and the selling prices of new single-detached housing built on those lots. In the introductory chapter, the upward climb over the years in the average price of building lots relative to the increase in new house prices is identified as a matter in need of closer study. The significance of this subject for planning practice is seen to lie in the power of planning authorities to intervene in the operation of property markets, and in the role of planning authorities implied in many proposals for solving the land price problem. In Chapter Two, numerous theoretical analyses and empirical studies of the determination and inter-temporal variation in residential land prices are surveyed. A critical assessment of the literature made in the first part of Chapter Three identifies several shortcomings. A static rather than dynamic approach, the assumption of market equilibrium and perfect competition, inadequate treatment of supply-demand interaction, and a limited behavioral content, characterize most of the works surveyed. A theoretical model is subsequently developed to explain the process by which residential lot prices are determined and change over time. Its fundamental hypothesis is that the level of new house prices and their changes over time are a prime determinant of lot prices and their intertemporal variation, while the profit-maximizing behavior of lot sellers and housebuilders generates the process by which lot prices increase over time. In Chapter Four, an empirical investigation is proposed for testing the theoretical model. Data on residential construction in Canada over the 1951-1977 period and financed under the provisions of the National Housing Act are selected for the investigation. Since the data pertain to a portion rather than the whole of the lot market, the theoretical model is reformulated in light of this and other empirical conditions. The Chapter is concluded with an outline of the statistical procedures to be used in the investigation. The results of the study are presented in Chapter Five. They are found to be generally consistent with the hypotheses of the empirical model, and the postulates of the theoretical model. It is concluded, among other things , that lot sellers and housebuilders behave in the manner proposed by the models, and that lot price increases are determined by house price increases. However, the validity of the model and wider application of the empirical findings are judged to be limited by the characteristics of the data used in the study. The concluding chapter offers several suggestions for future research on land prices and some implications for planning and public policy. The need for an improved economic understanding in urban planning is identified. A potential role is identified for planners in the provision of information in a market where imperfect information is a major source of observed market failure.

Brief aus Marseille, ETH-Bibliothek