Placement Conditions Research Articles

Experimental evaluation and optimization of improved conductivity of gelling acid etched fractures in deep, low-permeability reservoirs

Stimulation technology is the key to efficient development of deep low-permeability carbonate reservoirs. For such reservoirs, where the porosity and permeability are low, or where the reservoir is far from the borehole. An efficient production increase can only be achieved by using a deep percolation gelling acid fracture technique, maximizing the length of the acid etched fracture to expand the percolation area, and improving the conductivity of the acid etched fracture. A quantitative experimental study of the conductivity of acid etch fracture based on an acid rock tiling instrument, a 3D laser scanner, and an acid etch fracture conductivity evaluation device identified three typical supporting morphologies of gelling acid etch fracture walls: spot, line, and sheet. A systematic quantitative description and evaluation of the etch morphology of rocks etched by acid has been performed. The fracture morphology of acid etchings has been quantitatively evaluated under various experimental conditions such as fracture width, temperature, acid fluid consumption, displacement, and different acid fracture processes and their laws affecting fracture conductivity. The conductivity of acid corrosion fracture increases with the decrease of fracture width, and decreases with the increase of closure stress. The greater the amount of acid used, the higher the fracture conductivity; With the increase of flow Reynolds number, the conductivity of acid corrosion fracture shows a trend of increasing first and then decreasing. The fracture conductivity was compared and analyzed for different property placement conditions under the acid sand carrying technique, and the main effect of the acid etch fracture conductivity was identified. Optimization of high conductivity and deep penetration gelling acid fracturing techniques can help guide the design of acid fracturing and improve stimulation and recovery effects, thus achieving the goal of efficient development of deep, low permeability carbonate reservoirs to increase reserves and production.

Hydromechanical behavior of unsaturated swelling clays: review

Expansive soils are materials composed mainly of active minerals of the smectite family, where montmorillonite is an essential member of that group. These types of soils tend to undergo volumetric changes due to variations in moisture content. Many geotechnical engineering practices, such as dam core design or subgrade compaction, require a thorough evaluation of the response of these soils to determine placement conditions. However, the main problem in evaluating the mechanical response of this type of soil lies in the nonlinear nature, which limits the use of most classical constitutive models that apply the basic rules of elastoplasticity. In this study, an analysis is carried out to understand the hydromechanical behavior of expansive soils in saturated and unsaturated conditions. Direct and indirect physical evidence is presented and discussed to evaluate the hydraulic response of the soil structural elements responsible for these adverse dynamics from a global (expansive phenomena as a whole) and individual (swelling and shrinkage) perspective. Since the response of these soils is hydrostatic dependent, the locus of water movement in porous media is examined, starting from the Richards equation (1931), in order to consider the flow mechanisms in unsaturated media under transient conditions.

Quasi-Packing Different Spheres with Ratio Conditions in a Spherical Container

This paper considers the optimized packing of different spheres into a given spherical container under non-standard placement conditions. A sphere is considered placed in the container if at least a certain part of the sphere is in the container. Spheres are allowed to overlap with each other according to predefined parameters. Ratio conditions are introduced to establish correspondence between the number of packed spheres of different radii. The packing aims to maximize the total number of packed spheres subject to ratio, partial overlapping and quasi-containment conditions. A nonlinear mixed-integer optimization model is proposed for this ratio quasi-packing problem. A heuristic algorithm is developed that reduces the original problem to a sequence of continuous open dimension problems for quasi-packing scaled spheres. Computational results for finding global solutions for small instances and good feasible solutions for large instances are provided.

Gas flow characteristics of GCL under distortions, wet-dry cycles, and hydrating fluids

Geosynthetic clay liner (GCL) is commonly used in cover system of engineered landfill to limit migration of gases and infiltration of water. In engineered landfill, gas transfer occurs by advection and diffusion, which may take place at different time frames or simultaneously depending on placement conditions. Hence, efficacy of GCL as a gas barrier under advection and diffusion needs to be assessed at various geoenvironmental settings. In the present study, the gas flow response of GCL under advection and diffusion were evaluated at various apparent degrees of saturation, distortion levels, hydrating fluids, and wet-dry cycles using custom-designed test apparatus. Gas permeability and gas diffusion coefficient of GCL were found to decrease by four and three orders of magnitude respectively with an increase in apparent degree of saturation from 7% to 80%. Gas permeability and gas diffusion coefficient were increased with an increase in distortion levels. With an increase in wet-dry cycles 1 to 5, gas permeability and gas diffusion of GCL were increased marginally when hydrated with distilled water while increased by one order of magnitude for hydrated with 0.0125 M CaCl2 solution. The obtained results were compared with published results and found to be in good agreement.

Построение самопроверяемых цифровых устройств на основе модифицированных кодов Хэмминга с контролем самодвойственности вычисляемых функций

The article presents a methodology for optimizing transport costs with the use of modeling in PTV Visum software package. Based on the analysis of transport problems in large urban agglomerations, a quality criterion was chosen for the assessment of passenger transport performance. An approach has been proposed to introduce transport hub systems with the purpose to minimize time spending on transfer, in particular, and on trip by public transport in a whole. This optimization method for transport spending represents an algorithm of 3 key blocks: the formation of transport model for being studied agglomeration, the placement conditions and the choice of transport hub locations. The model is formed on the base of 4-step approach, the trips distribution in a network is based on entropy approach which is considered in the second section in more details. The placement conditions go from an idea to minimize time total spending on moving, the number of hubs being introduced is limited by their construction financing. The approach application is demonstrated on the example of northwestern urban agglomeration Sertolovo-Osinovaya Roshcha-Pargolovo which represents being actively built-up residential districts on St. Petersburg city border. The specificities of its transport network, including also hubs and highways with complicated traffic, are determined. Based on open sources and statistical data, a transport model was developed, its calibration was pursued. 3 options for placing transport hubs on network of the agglomeration are presented. As a result of the research, the analysis for the options of transport hub placements is presented and the most promising option from the view of purpose meaning achievement for hub placement in being considered agglomeration is proposed.

Формирование системы транспортно-пересадочных узлов в городской агломерации

The article presents a methodology for optimizing transport costs with the use of modeling in PTV Visum software package. Based on the analysis of transport problems in large urban agglomerations, a quality criterion was chosen for the assessment of passenger transport performance. An approach has been proposed to introduce transport hub systems with the purpose to minimize time spending on transfer, in particular, and on trip by public transport in a whole. This optimization method for transport spending represents an algorithm of 3 key blocks: the formation of transport model for being studied agglomeration, the placement conditions and the choice of transport hub locations. The model is formed on the base of 4-step approach, the trips distribution in a network is based on entropy approach which is considered in the second section in more details. The placement conditions go from an idea to minimize time total spending on moving, the number of hubs being introduced is limited by their construction financing.
 The approach application is demonstrated on the example of northwestern urban agglomeration Sertolovo-Osinovaya Roshcha-Pargolovo which represents being actively built-up residential districts on St. Petersburg city border. The specificities of its transport network, including also hubs and highways with complicated traffic, are determined. Based on open sources and statistical data, a transport model was developed, its calibration was pursued. 3 options for placing transport hubs on network of the agglomeration are presented. As a result of the research, the analysis for the options of transport hub placements is presented and the most promising option from the view of purpose meaning achievement for hub placement in being considered agglomeration is proposed.

Role of Clay Mineralogy in the Estimation of Permeability Coefficient in Compacted Fine-grained Soils

The foundations constructed upon the soils are depending upon the three major criteria i.e., strength, stiffness, and stability. In all three cases, the subsoil is expected to be in a compacted state. In coarse-grained soils, the result of compaction is a problem of substantiality, whereas physicochemical sort of response for fine soils. There is comparatively limited research known about the effects of clay mineralogy on the permeability properties of fine-grained soils, as well as different placement conditions and energy levels. In this study, consolidation behavior will be estimated for the six field soils and one artificial soil having different liquid limits, the Mineralogical composition of clay, and its plasticity properties under placement conditions like 95% of the γd max on dry and wet sides, and at OMC. The permeability behavior of these soils under study is computed by calculating the IS Light and Heavy Compaction energy levels' corresponding consolidation properties (Cv and Mv) using five practical approaches that have been described in the literature. The coefficient of permeability (K) of soils is calculated accurately with a fair degree of accuracy by 1-D consolidation test data like Cv and Mv. The estimated values of K were compared with the K values obtained from experimental studies under various stages of loading, and it was observed that there was good agreement between the two. These results were validated using Abaqus software through Finite Element Modelling analysis.

The Use of a Single-Time Sit-To-Stand Test in Ambulatory Individuals With Spinal Cord Injury by Primary Health Care Providers.

The uncertain health care situations, such as that created by the COVID-19 pandemic, has limited hospital access and facilitated a paradigm shift in health care toward an increased demand for standard home visits and community-based rehabilitation services, including by ambulatory individuals with spinal cord injury (SCI). This 6-month prospective study explored the validity and reliability of a single-time sit-to-stand (STSTS) test when used by primary health care (PHC) providers, including a village health volunteer, caregiver, individual with SCI, and health professional. Eighty-two participants were assessed for the STSTS using four arm placement conditions (arms on a walking device, arms on knees, arms free by the sides, and arms crossed over the chest) and standard measures, with prospective fall data follow-up over 6 months. Thirty participants involved in the reliability study were also assessed and reassessed for the ability to complete the STSTS conditions by PHC providers. Outcomes of the STSTS test, except the condition with arms on a walking device, could significantly discriminate lower extremity muscle strength (LEMS) and mobility of the participants (rpb = -0.58 to 0.69) with moderate concurrent validity. Outcomes of the tests without using the arms also showed moderate to almost-perfect reliability (kappa = 0.754-1.000) when assessed by PHC raters. The findings suggest the use of an STSTS with arms free by the sides as a standard practical measure by PHC providers to reflect LEMS and mobility of ambulatory individuals with SCI in various clinical, community, and home-based settings.

Leveraging Multiple Distinct EEG Training Sessions for Improvement of Spectral-Based Biometric Verification Results.

Most studies on EEG-based biometry recognition report results based on signal databases, with a limited number of recorded EEG sessions using the same single EEG recording for both training and testing a proposed model. However, the EEG signal is highly vulnerable to interferences, electrode placement, and temporary conditions, which can lead to overestimated assessments of the considered methods. Our study examined how different numbers of distinct recording sessions used as training sessions would affect EEG-based verification. We analyzed the original data from 29 participants with 20 distinct recorded sessions each, as well as 23 additional impostors with only one session each. We applied raw coefficients of power spectral density estimate, and the coefficients of power spectral density estimate converted to the decibel scale, as the input to a shallow neural network. Our study showed that the variance introduced by multiple recording sessions affects sensitivity. We also showed that increasing the number of sessions above eight did not improve the results under our conditions. For 15 training sessions, the achieved accuracy was 96.7 ± 4.2%, and for eight training sessions and 12 test sessions, it was 94.9 ± 4.6%. For 15 training sessions, the rate of successful impostor attacks over all attack attempts was 3.1 ± 2.2%, but this number was not significantly different from using six recording sessions for training. Our findings indicate the need to include data from multiple recording sessions in EEG-based recognition for training, and that increasing the number of test sessions did not significantly affect the obtained results. Although the presented results are for the resting-state, they may serve as a baseline for other paradigms.

Pre-applied mechanically bonded waterproofing membranes: Bond strength of nonwovens to concrete and influencing parameters

Pre-applied bonded membranes are used for waterproofing on the outside of concrete basements and are installed prior to the reinforcement, e.g., on a formwork. They often use nonwovens as a bonding layer and must ensure a sufficient bond both during stripping and use. However, it is not yet known how the bond develops and how it depends on concrete placement conditions. Hence, this study tested ten nonwovens for their bond to concrete in pull-off tests according to DIN EN 1542, varying the fresh concrete and concrete placement. The bond strength for all nonwovens developed proportionally to the concrete tensile splitting strength at a factor of 18–56% and was, e.g., 0.40–0.78 MPa after two days. The development was approximated by a fib model code approach, with higher concrete tensile splitting strengths and lighter nonwovens resulting in better bond strengths. In comparison with the reference tests, the bond strength was reduced for larger distances to the internal vibrator (max. −35%), higher w/c ratios of the fresh concrete, and nonwovens with higher basis weights. Also, water movements and air voids deviated the bond strength of vertically oriented nonwovens by −25% to +35% compared to reference values. Video recordings and measurements of the w/s ratio in the nonwoven complemented the results and showed that the nonwovens behave similarly to Controlled Permeable Formworks and separate excess water from the fresh concrete. As a result, the w/c ratio of the cement paste in the bonding zone changes, affecting the bond strength.

The volatile release evaluation of nicotine from snus products under different storage conditions based on surface-enhanced Raman spectroscopy technology.

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive analytical detection technique that provides unique chemical and structural information on target molecules. Snus is a type of tobacco product that can release nicotine and other components under certain humidity and temperature without burning, and the evaluation of its nicotine release under different storage conditions is very important for understanding its characteristics, regulating its components, and setting reasonable storage conditions. Herein, by means of an artificial climate box and suction extraction device, the volatile release evaluations of nicotine from snus products under different storage conditions were performed based on Fe3O4 microparticles coated with Au nanorods and Au nanoparticles (Fe3O4@AuNRsNPs) as SERS substrates combined with a capillary. The Fe3O4@AuNRsNPs assemblies can be fixed in the inner wall of the capillary with the aid of an external magnetic field, which improved the maneuverability of the SERS substrates. By comparing the intensities of the spectral peaks of the symmetrical breathing of the pyridine moiety of nicotine molecules with increasing temperature and humidity, which could significantly accelerate the volatile release of a small amount of nicotine, the nicotine release under different conditions could be evaluated. Based on this strategy, it was possible to obtain the storage or placement conditions of the product. The results of this study provide a reference to clarify the volatile release of nicotine under various storage conditions, which is helpful for better regulation of the levels of nicotine in snus. Moreover, such destruction-free evaluation of the volatile release of nicotine from snus products under different storage conditions opens up new perspectives for further research about the impact of nicotinoids on smokers' health and cessation programs.

Bioabsorbable, elastomer-coated magnesium alloy coils for treating saccular cerebrovascular aneurysms

Cerebral aneurysm embolization is a therapeutic approach to prevent rupture and resultant clinical sequelae. Current, non-biodegradable metallic coils (platinum or tungsten) are the first-line choice to secure cerebral aneurysms. However, clinical studies report that up to 17% of aneurysms recur within 1 year after coiling, leading to retreatment and additional surgery. It would be ideal for the aneurysm coiling material to induce acute thrombotic occlusion, contribute to a tissue development process to fortify the degenerated vessel wall, and ultimately resorb to avoid leaving a permanent foreign body. With these properties in mind, a new fatty amide-based polyurethane urea (PHEUU) elastomer was synthesized and coated on biodegradable metallic (Mg alloy) coils to prepare a bioabsorbable cerebral saccular aneurysm embolization device. The chemical structure of PHEUU was confirmed using two-dimensional nuclear magnetic resonance spectroscopy. PHEUU showed comparable physical properties to elastomeric biodegradable polyurethanes lacking fatty amide immobilization, modest enzymatic degradation profiles in the first 8 wks, inherent antioxidant activity (>70% at 48 h), no cytotoxicity, and better protection for the underlying Mg alloy than poly(lactic-co-glycolic acid) (PLGA) against surface corrosion and cracking. Rat aortic smooth muscle cell attachment and platelet deposition were higher with the PHEUUs compared to bare or PLGA coated Mg alloy in vitro. PHEUU-coated Mg alloy coils showed the potential to design a fully bioabsorbable embolization coil amenable to clinical placement conditions based on computational mechanics modeling and blood-contacting test using an in vitro aneurysm model. In vivo studies using a mouse aneurysm model elicited comparable inflammatory cytokine expression to a commercially available platinum coil.

Special issue on PID control in the information age: Theoretical advances and applications

Special issue on PID control in the information age: Theoretical advances and applications

Long-Term Performance of Liners Subjected to Freeze-Thaw Cycles

The technique of using clay-sand mixtures as liners has been widely used in several geotechnical projects where hydraulic barriers or waste-buffer layers are required. During weather fluctuations and below-zero temperature conditions, these layers can be subjected to successive freeze-thaw cycles. The serviceability of such liners needs to be examined during their lifetime for efficiency and function under such suspected weather conditions. The hydraulic conductivity over the long run needs to remain within the acceptable design ranges. In this study, the efficiency of two different clay-sand liners were examined under the effect of freeze-thaw cycles for extended serviceability. The hydraulic conductivity under a continuous discharge rate of these layers was measured before and after applying 15 successive freeze-thaw cycles for more than half a year. The results indicate dramatic changes in the hydraulic conductivity parameter for the specimens subjected to freeze-thaw cycles depending on their mineralogical composition and applied stress. These changes were found to be related to the sealed material composition and placement conditions. The data obtained were found of interest and can be utilized for evaluating the efficiency of the liners in areas subjected to extreme environmental exposures including freeze conditions over extended periods.

АНАЛИЗ ВОЗМОЖНОСТЕЙ ФИЛЬТРУЮЩЕГО РЫБОЗАЩИТНОГО УСТРОЙСТВА ПРИ ГОРИЗОНТАЛЬНОМ РАЗМЕЩЕНИИ КАССЕТ

Problem statement. In accordance with the code of rules (SP 101.13330.2012), the use of fish protection devices with a filter screen and a flushing system applies to water intake facilities in various placement conditions, in this regard, it is relevant to expand the possibilities of using filter cassettes at shallow water depths in the water source.
 Results. A methodology has been developed to substantiate the filler parameters of a horizontal filter cassette in the form of plastic balls and their distribution along its length, as well as a preliminary assessment of the uniformity of flow rates over the area of the filter cassette.
 Conclusions. To improve the operational characteristics of the filter fish-protective device in conditions of shallow water sampling depths, instead of the basic design with a vertical cassette layout, a filter cassette with a horizontally positioned water intake surface and a self-washing effect is recommended, in which a filler made of plastic balls (with positive buoyancy) is used and there is free space for their vertical movement. On the basis of hydraulic calculation, a method for preliminary estimation of filtration rates in such a cassette has been developed. To ensure a uniform distribution of the filtration rates of the water flow along the length of the cassette, it is recommended to use balls of different diameters. Evaluation of the working conditions of the cassette allowed us to obtain a pattern of changes in the diameter of the balls along its length, so for a specific example, the calculated diameter of the balls varied from 8 mm, in the suction nozzle, to 40 mm at the end of the cassette. The technique can be used to calculate the parameters of horizontal filter cassettes of fish protection devices.

Tracking Fluorine during Aqueous Photolysis and Advanced UV Treatment of Fluorinated Phenols and Pharmaceuticals Using a Combined 19F-NMR, Chromatography, and Mass Spectrometry Approach.

Fluorine incorporation into organic molecules has increased due to desirable changes in the molecular physiochemical properties. Common fluorine motifs include: aliphatic fluorines and -CF3, or -F containing groups bonded directly onto an aromatic (Ar-CF3 and Ar-F) or heteroaromatic ring. Photolysis of these compounds, either in natural or engineered systems, is a potential source of new fluorinated byproducts. Given the potential persistence and toxicity of fluorinated byproducts, monitoring of product formation during photolysis of various fluorinated motifs is needed. 19F-NMR is a means to detect and quantify these species. Ar-CF3 and Ar-F model compounds (2-, 3-, and 4-(trifluoromethyl)phenol, 2-, 3-, 4-fluorophenol, and 2,6-, 3,5-difluorophenol) were photolyzed under a variety of aqueous conditions: pH 5, pH 7, pH 10, 1 mM H2O2 at pH 7 to form •OH, and 0.5 mM SO3 2- at pH 10 to form eaq -. Pharmaceuticals with the Ar-CF3 (fluoxetine) and Ar-F plus pyrazole-CF3 (sitagliptin) motifs were treated similarly. Parent molecule concentrations were monitored with high pressure liquid chromatography with a UV detector. Fluorine in the parent and product molecules was quantified with 19F-NMR and complete fluorine mass balances were obtained. High resolution mass spectrometry was used to further explore product identities. The major product for Ar-F compounds was fluoride. The Ar-CF3 model compounds led to fluoride and organofluorine products dependent on motif placement and reaction conditions. Trifluoroacetic acid was a product of 4-(trifluoromethyl)phenol and fluoxetine. Additional detected fluoxetine products identified using mass spectrometry resulted from addition of -OH to the aromatic ring, but a dealkylation product could not be distinguished from fluoxetine by 19F-NMR. Sitagliptin formed multiple products that all retained the pyrazole-CF3 motif while the Ar-F motif produced fluoride. 19F-NMR, mass spectrometry, and chromatography methods provide complementary information on the formation of fluorinated molecules by modification or fragmentation of the parent structure during photolysis, allowing screening for fluorinated photoproducts and development of fluorine mass balances.

Propofol-an alternative to sevoflurane for laryngeal mask airway insertion in children

Supraglottic devices like laryngeal mask airway (LMA) is used in children for anesthesia as it induces least hemodynamic stress response. We have carried out this trial to measure the potency of induction agents like propofol with sevoflurane for conditions of LMA placement in pediatric surgery. 60 children were included in our study and were split into two groups. Children in group S were induced with sevoflurane 8vol%. Children in group P were induced with propofol at 3 mg/kg IV. Proper size of LMA was inserted. Induction time, insertion time, LMA placement conditions and hemodynamic abnormalities were assessed. Induction time was shorter with group P contrary to S group. (p<0>0.05) There was no remarkable difference in various LMA insertion conditions and LMA insertion score in both groups. Hemodynamic changes were comparable in group S and P. Propofol and sevoflurane revealed equivalent and suitable LMA placement settings. So propofol may be a good substitute to sevoflurane for placement of LMA in children in a recourse limited setting. Keywords: Sevoflurane, Propofol, Laryngeal mask airway, Children.

The Doctrinal Inconsistencies in Claims for Compensation for Accommodation Conditions that Infringe Fundamental Rights

The criticism of the current regulation of the compensation procedure under the Prison Act can be given in the legal-dogmatic contradiction and the imprecision of the normative text. The latter inaccuracies have led to the different interpretation of the law by the judiciary in the penal and civil fields. In conclusion, therefore, if the claim to be enforced is related to the circumstances of the placement which violate fundamental rights, it is possible, as explained above, to bring an action only for the enforcement of objective sanctions for violation of personal rights, but not for damages in addition to sanctions independent of the responsibility. Civil proceedings under the general rules are only possible if the claim is not related to accommodation conditions which infringe fundamental rights. In such a case, however, it must be borne in mind that, under Article 143 subsection (1) to (2) of the Prison Act, a prisoner cannot bring a claim for damages against a prison directly before a court: he must bring it before the prison authorities where the damage occurred. The prisoner may appeal against this decision within a time limit of 30 days from the date of notification. Only in the case of a claim for damages arising from a violation of personal rights (i.e. not linked to an injury caused by conditions of detention which infringe the prohibition of torture, cruel, inhuman or degrading treatment), it is possible to go directly to court and the action does not have to be preceded by proceedings before the penitentiary institution. In our view, it would be worthwhile to reintroduce the possibility to claim for harm caused by placement conditions that violate fundamental rights into the framework of civil litigation. However, this would require the creation of a legal environment which does not give rise to the abovementioned dogmatic contradictions. It should be pointed out, by way of example, that the ECtHR does not wish to introduce a separate, formalised procedure for compensating detainees, but is “content” with the possibility of bringing a civil action based on a violation of personal rights.

Experimental Study of the Bearing Capacity of Footings on Stiff Clay Overlying Very Loose Sand

Experimental model tests were carried out to study the bearing capacity of footings on stiff clay overlying very loose sand. Emphasis was given to the effects of the thickness of the clay (H) relative to the footing size (D). The clay thickness was fixed during the experiments and the foundation was represented by rigid circular steel plates of different sizes to give H/D ratios ranging from 0.6 to 2.0. The shear parameters of the two soils were measured in the laboratory at their placement conditions. The load tests were carried out to failure. The load settlement curves showed non-linear relationship. The ultimate bearing capacity decreased with increasing plate diameter. For the same plate (150mm) the bearing capacity on homogeneous stiff clay is more than twice that of the stiff clay overlying loose sand. The bearing capacity factor Nc was back-calculated from the results of the model tests. The very loose sand caused the factor to decrease to values less than 3.0 for H/D smaller than 1.0. The effective depth which is the smallest thickness of the stiff clay that does not allow the lower layer to affect bearing capacity is greater than twice the plate diameter (> 2D).

Lens dose reduction with a bismuth shield in neurocone-beam computed tomography: an investigation on optimum shield device placement conditions.

This study aimed to determine the placement distance, number, and position of the bismuth shield for developing a lens protective device for cone-beam computed tomography (CBCT). To determine the dose reduction rate, the lens doses were measured using an anthropomorphic head phantom and a real-time dosimeter. The image quality assessment was determined by analyzing the change in the pixel value, caused by the bismuth shield, and the artifact index was calculated from the pixel value and image noise within various regions of interest in the head phantom. When the distance between the bismuth shield and the subject was increased, the image quality deteriorated less, but there was also a decrease in the lens dose reduction rate. Upon changing the number of bismuth shields from 1-ply to 2-ply, the dose reduction rate increased; however, there was a decrease in the image quality. Additionally, placing the bismuth shield outside of the subject improved the dose reduction rate without deteriorating the image quality. The optimum placement conditions of the bismuth shield were concluded as follows: positioned outside, placed 10mm from the surface of the subject, and used a 1-ply bismuth shield. When these placement conditions were used, the lens dose reduction rate was 26.9 ± 0.36% (right-left average) for the "bismuth shield: separate". The protective device developed in this study will contribute to radiation dose reduction in CBCT scans.