Least Squares Support Vector Machine Kalman Filter for Physiological Tremor Suppression in Minimally Invasive Surgical Robot

This paper studies the physiological tremor filtering in minimally invasive surgical robot.The surgeon􀆳s physiological tremor of the hand can cause the vibration of the tip of the surgical instrument,which may reduce operative accuracy and limit the application of surgical robots.Aiming at the vibration caused by physiological tremor of hand,we propose a Least Squares Support Vector Machine Kalman Filter(LSSVMKF),which can filter the tremor by estimating and modeling the tremor signal by Kalman filter and then superimposing it reversely in the control signal.When estimating and modeling the tremor signal,the filter uses the Least Squares Support Vector Machine(LS⁃SVM)to build the regression model of the constant parameters(Process Noise Covariance and Measurement Noise Covariance)of the traditional Kalman filter,which can dynamically adjust these parameters during the operation and improve the accuracy of Kalman filter.The simulation results show that the LSSVMKF can effectively filter out the tremor signal,thereby improving the accuracy of surgery.

Method for Latency Measurement of Visual Feedback-Based Master–Slave Minimally Invasive Surgical Robot

To measure the latency between human motion stimulation and stereo image display response in a visual feedback-based minimally invasive surgical(MIS) robotic system,a method was proposed by comparing the orientations of input and output events through image-processing technology. This method used a black bar to keep pace with the measured joint rotating at a number of speeds. During tests,an external camera was placed in front of the apparatus with a proper visual field,so that it can simultaneously view orientations of both bars fixed on the corresponding joints. After quantitatively analyzing the accuracy of the proposed measurement method,the method was applied to a visual feedback-based master–slave robotic system with two-degrees-of-freedom. Experimental results show that the latency of the overall system was approximately 250 ms,and the opposite clearance of the measured joint was in the range of 1.7°–1.9°.

Shape Sensing for Single-Port Continuum Surgical Robot Using FewMulticore Fiber Bragg Grating Sensors

We proposed a method for shape sensing using a few multicore fiber Bragg grating (FBG) sensors ina single-port continuum surgical robot (CSR). The traditional method of utilizing a forward kinematic model tocalculate the shape of a single-port CSR is limited by the accuracy of the model. If FBG sensors are used forshape sensing, their accuracy will be affected by their number, especially in long and flexible CSRs. A fusionmethod based on an extended Kalman filter (EKF) was proposed to solve this problem. Shape reconstructionwas performed using the CSR forward kinematic model and FBG sensors, and the two results were fused usingan EKF. The CSR reconstruction method adopted the incremental form of the forward kinematic model, whilethe FBG sensor method adopted the discrete arc-segment assumption method. The fusion method can eliminatethe inaccuracy of the kinematic model and obtain more accurate shape reconstruction results using only a smallnumber of FBG sensors. We validated our algorithm through experiments on multiple bending shapes underdifferent load conditions. The results show that our method significantly outperformed the traditional methodsin terms of robustness and effectiveness.

Progress in Force-Sensing Techniques for Surgical Robots

Force sensing is vital for situational awareness and safe interaction during minimally invasive surgery.Consequently,surgical robots with integrated force-sensing techniques ensure precise and safe operations.Over the past few decades,there has been considerable progress in force-sensing techniques for surgical robots.This review summarizes the existing electrically-and optically-based force sensors for surgical robots,including piezoresistive,piezoelectric,capacitive,intensity/phase-modulated,andfiber Bragg gratings.Their principles,applications,advantages,and limitations are also discussed.Finally,we summarize our conclusions regarding state-of-the-art force-sensing technologies for surgical robotics.

Robotic versus laparoscopic surgery for sporadic benign insulinoma:Short-and long-term outcomes

Background:Minimally invasive surgery is the optimal treatment for insulinoma.The present study aimed to compare short-and long-term outcomes of laparoscopic and robotic surgery for sporadic benign insulinoma.Methods:A retrospective analysis of patients who underwent laparoscopic or robotic surgery for insulinoma at our center between September 2007 and December 2019 was conducted.The demographic,perioperative and postoperative follow-up results were compared between the laparoscopic and robotic groups.Results:A total of 85 patients were enrolled,including 36 with laparoscopic approach and 49 with robotic approach.Enucleation was the preferred surgical procedure.Fifty-nine patients(69.4%)underwent enucleation;among them,26 and 33 patients underwent laparoscopic and robotic surgery,respectively.Robotic enucleation had a lower conversion rate to laparotomy(0 vs.19.2%,P=0.013),shorter operative time(102.0 vs.145.5 min,P=0.008)and shorter postoperative hospital stay(6.0 vs.8.5 d,P=0.002)than laparoscopic enucleation.There were no differences between the groups in terms of intraoperative blood loss,the rates of postoperative pancreatic fistula and complications.After a median follow-up of 65 months,two patients in the laparoscopic group developed a functional recurrence and none of the patients in the robotic group had a recurrence.Conclusions:Robotic enucleation can reduce the conversion rate to laparotomy and shorten operative time,which might lead to a reduction in postoperative hospital stay.

Robotic-assisted low anterior resection for rectal cancer shows similar clinical efficacy to laparoscopic surgery: A propensity score matched study

BACKGROUND Rectal cancer ranks as the second leading cause of cancer-related mortality worldwide,necessitating surgical resection as the sole treatment option.Over the years,there has been a growing adoption of minimally invasive surgical techni-ques such as robotic and laparoscopic approaches.Robotic surgery represents an innovative modality that effectively addresses the limitations associated with traditional laparoscopic techniques.While previous studies have reported favo-rable perioperative outcomes for robot-assisted radical resection in rectal cancer patients,further evidence regarding its oncological safety is still warranted.AIM To conduct a comparative analysis of perioperative and oncological outcomes between robot-assisted and laparoscopic-assisted low anterior resection(LALAR)procedures.METHODS The clinical data of 125 patients who underwent robot-assisted low anterior resection(RALAR)and 279 patients who underwent LALAR resection at Shandong Provincial Hospital Affiliated to Shandong First Medical University from December 2019 to November 2022 were retrospectively analyzed.After performing a 1:1 propensity score matching,the patients were divided into two groups:The RALAR group and the LALAR group(111 cases in each group).Subsequently,a comparison was made between the short-term outcomes within 30 d after surgery and the 3-year survival outcomes of these two groups.RESULTS Compared to the LALAR group,the RALAR group exhibited a significantly earlier time to first flatus[2(2-2)d vs 3(3-3)d,P=0.000],as well as a shorter time to first fluid diet[4(3-4)d vs 5(4-6)d,P=0.001].Additionally,the RALAR group demonstrated reduced postoperative indwelling catheter time[2(1-3)d vs 4(3-5)d,P=0.000]and decreased length of hospital stay after surgery[5(5-7)d vs 7(6-8)d,P=0.009].Moreover,there was an observed increase in total cost of hospitalization for the RALAR group compared to the LALAR group[10777(10780-11850)dollars vs 10550(8766-11715)dollars,P=0.012].No significant differences were found in terms of conversion rate to laparotomy or incidence of postoperative complications between both groups.Furthermore,no significant disparities were noted regarding the 3-year overall survival rate and 3-year disease-free survival rate between both groups.CONCLUSION Robotic surgery offers potential advantages in terms of accelerated recovery of gastrointestinal and urologic function compared to LALAR resection,while maintaining similar perioperative and 3-year oncological outcomes.

State-of-the-art of intelligent minimally invasive surgical robots Masakatsu

A number of developed countries are rapidly turning into super-aged societies.Consequently,the demand for reduced surgical invasiveness and enhanced efficiency in the medical field has increased due to the need to reduce the physical burden on older patients and shorten their recovery period.Intelligent surgical robot systems offer high precision,high safety,and reduced invasiveness.This paper presents a review of current intelligent surgical robot systems.The history of robots and three types of intelligent surgical robots are discussed.The problems with current surgical robot systems are then analyzed.Several aspects that should be considered in designing new surgical systems are discussed in detail.The paper ends with a summary of the work and a discussion of future prospects for surgical robot development.

Review of surgical robotic systems for keyhole and endoscopic procedures:state of the art and perspectives

Minimally invasive surgery,including laparoscopic and thoracoscopic procedures,benefits patients in terms of improved postoperative outcomes and short recovery time.The challenges in hand–eye coordination and manipulation dexterity during the aforementioned procedures have inspired an enormous wave of developments on surgical robotic systems to assist keyhole and endoscopic procedures in the past decades.This paper presents a systematic review of the state-of-the-art systems,picturing a detailed landscape of the system configurations,actuation schemes,and control approaches of the existing surgical robotic systems for keyhole and endoscopic procedures.The development challenges and future perspectives are discussed in depth to point out the need for new enabling technologies and inspire future researches.

Development of a novel hand-eye calibration for intuitive control of minimally invasive surgical robot

Robotic-assisted surgical system has introduced a powerful platform through dexterous instrument and hand-eye coordination intuitive control.The knowledge of laparoscopic vision is a crucial piece of information for robot-assisted minimally invasive surgery focusing on improved surgical outcomes.Obtaining the transformation with respect to the laparoscope and robot slave arm frames using hand-eye calibration is essential,which is a key component for developing intuitive control algorithm.We proposed a novel two-step modified dual quaternion for hand-eye calibration in this study.The dual quaternion was exploited to solve the hand-eye calibration simultaneously and powered by an iteratively separate solution.The obtained hand-eye calibration result was applied to the intuitive control by using the hand-eye coordination criterion.Promising simulations and experimental studies were conducted to evaluate the proposed method on our surgical robot system.We extensively compared the proposed method with state-of-the-art methods.Results demonstrate this method can improve the calibration accuracy.The effectiveness of the intuitive control algorithm was quantitatively evaluated,and an improved hand-eye calibration method was developed.The relationship between laparoscope and robot kinematics can be established for intuitive control.

A compliant surgical robotic instrument with integrated IPMC sensing and actuation

Robotic assisted surgery is becoming widely adopted by surgeons for a number of reasons,which include improved instrumentation control and dexterity as well as faster patient recovery times and cosmetic advantages.Robotic assisted surgery is currently one of the fastest growing applications in robotics.Although the traditional robotic actuators which are currently used have advanced performance which can,in some aspects,surpass that of humans,they simply do not have the capabilities and diversity required to meet the demand for new applications in robotic surgery.Novel transducers which have advanced capabilities and which allow safe operation in delicate environments are needed.Ionic polymer-metal composites(IPMCs)have extensive desirable characteristics when compared with traditional actuators and as their transduction mechanisms can mimic biological muscle they have much potential for future advanced biomedical and surgical robotics.In this research,a complete two degree-of-freedom(2DOF)surgical robotic instrument has been developed,which with the attachment of surgical tools(scalpel,etc.)has the ability to undertake surgical procedures.The system integrates an IPMC sensor and actuator at each joint.A gain scheduled(GS)controller,which is tuned with an iterative feedback tuning(IFT)algorithm,has been developed to ensure an accurate and adaptive response.The main advantages of this device over traditional devices are the improved safety through a natural compliance of the joints as well as the mechanical simplicity which ensures ease of miniaturisation for minimally invasive surgery(MIS).The components of the system have been tested and shown to have the capabilities required to operate the device for certain surgical procedures,specifically a device work envelope of 1600 mm^(2),compliance of 0.0668 m/N while still maintaining enough force to cut tissue,IPMC sensor accuracy between 3-22%and a control system which has shown to guarantee zero steady state error.

Initial experience of laparoendoscopic single-site radical prostatectomy with a novel purpose-built robotic system

Objective This prospective single-arm clinical trial aimed to evaluated the feasibility and safety of the application of the SHURUI system(Beijing Surgerii Technology Co.,Ltd.,Beijing,China),a novel purpose-built robotic system,in single-port robotic radical prostatectomy.Methods Sixteen patients diagnosed with prostate cancer were prospectively enrolled in and underwent robotic radical prostatectomy from October 2021 to August 2022 by the SHURUI single-port robotic surgical system.The demographic and baseline data,surgical,oncological,and functional outcomes as well as follow-up data were recorded.Results The mean operative time was 226.3(standard deviation[SD]52.0)min,and the mean console time was 183.4(SD 48.3)min,with the mean estimated blood loss of 116.3(SD 90.0)mL.The mean length of postoperative hospital stay was 4.50(SD 0.97)days.Two patients had postoperative complications(Clavien-Dindo Grade II),and both patients improved after conservative treatment.All patients’postoperative prostate-specific antigen levels decreased to below 0.2 ng/mL 1 month after discharge.The mean prostate-specific antigen level further decreased to a mean of 0.0219(SD 0.0641)ng/mL 6 months after surgery.Thirty days postoperatively,12 out of 16 patients reported using no more than one urinary pad per day,and all patients reported satisfactory urinary control without the need for pads 6 months after surgery.Conclusion The SHURUI system is safe and feasible in performing radical prostatectomy via both transperitoneal and extraperitoneal approaches.Tumor control and urinary continence were satisfying for patients enrolled in.The next phase involves conducting a large-scale,multicenter randomized controlled trial to thoroughly assess the effectiveness and safety of the new technology in a broader population.

Robotic surgery for multi-visceral resection in locally advanced colorectal cancer:Techniques,benefits and future directions

Colorectal cancer accounts for 10%of diagnosed cancers globally and often presents as advanced disease,necessitating aggressive treatment.With both younger and healthier elderly patients being diagnosed,as well as potentially the need for salvage therapy post total neoadjuvant treatment,surgical options for cure include pelvic exenteration.Whilst typically performed via an open approach,there has been an increased utilisation of minimally invasive techniques including robotic surgery.Offering smaller in-cisions,reduced postoperative pain,and quicker recovery time than open surgery,robotic techniques have demonstrated lower blood loss,shorter hospital stays,and reduced morbidity.Moreover,the er-gonomic design of robotic systems provides surgeons with comfort during long procedures and increased precision.It also offers an increased opportunity for organ preservation and reconstruction whilst maintaining adequate oncological outcomes.As robotic technology continues to evolve and combines with artificial intelligence,it is poised to play an even more significant role in the management of complex colorectal cancer cases,improving survival and long-term outcomes.

Robot-Assisted Nephrotomy as a Nephron-Sparing Approach for Completely Intraparenchymal Renal Tumors

Introduction: The diagnosis of small renal masses and the endophytic tumor approach have become challenging. This study aims to describe exclusively robot-assisted surgery as an alternative nephron-sparing approach for renal intraparenchymal tumors. Patients and Methods: We retrospectively analyzed all patients with completely endophytic tumors undergoing robot-assisted partial nephrectomy, treated under the Da Vinci System®, aided by intraoperative ultrasound. The patients’ demographic characteristics, perioperative and oncological outcomes were assessed. Results: From a total of 13 partial nephrectomies performed between 06/2010 and 10/2021, all patients underwent nephrotomy. The patients’ mean age was 52 years and the tumor measured mean 2.6 cm. Warm ischemia time was 24 minutes and histopathological analysis revealed that 12 patients had renal cell carcinoma. In a mean 36-month follow-up, no significant renal function alterations were found and no local or systemic recurrences occurred. Conclusion: Robot-assisted access is a safe and effective option for the nephron-sparing technique in completely intraparenchymal renal tumors.

Feasibility and safety of minimally invasive multivisceral resection for T4b rectal cancer:A 9-year review

BACKGROUND Colorectal cancer is the third most common cancer and the second highest cause of cancer-related mortality worldwide.About 5%-10%of patients are diagnosed with locally advanced rectal cancer(LARC)on presentation.For LARC invading into other structures(i.e.T4b),multivisceral resection(MVR)and/or pelvic ex-enteration(PE)remains the only potential curative surgical treatment.MVR and/or PE is a major and complex surgery with high post-operative morbidity.Minimally invasive surgery(MIS)has been shown to improve short-term post-operative outcomes in other gastrointestinal malignancies,but there is little evi-dence on its use in MVR,especially so for robotic MVR.This is a single-center retrospective cohort study from 1st January 2015 to 31st March 2023.Inclusion criteria were patients diagnosed with cT4b rectal cancer and underwent MVR,or stage 4 disease with resectable systemic metastases.Pa-tients who underwent curative MVR for locally recurrent rectal cancer,or me-tachronous rectal cancer were also included.Exclusion criteria were patients with systemic metastases with non-resectable disease.All patients planned for elective surgery were enrolled into the standard enhanced recovery after surgery pathway with standard peri-operative management for colorectal surgery.Complex sur-gery was defined based on technical difficulty of surgery(i.e.total PE,bladder-sparing prostatectomy,pelvic lymph node dissection or need for flap creation).Our primary outcomes were the margin status,and complication rates.Cate-gorical values were described as percentages and analysed by the chi-square test.Continuous variables were expressed as median(range)and analysed by Mann-Whitney U test.Cumulative overall survival(OS)and recurrence-free survival(RFS)were analysed using Kaplan-Meier estimates with life table analysis.Log-rank test was performed to determine statistical significance between cumulative estimates.Statistical significance was defined as P<0.05.Meier estimates with life table analysis.Log-rank test was performed to determine statistical significance between cumulative estimates.Statistical significance was defined as P<0.05.RESULTS A total of 46 patients were included in this study[open MVR(oMVR):12(26.1%),miMVR:36(73.9%)].Patients’American Society of Anesthesiologists score,body mass index and co-morbidities were comparable between oMVR and miMVR.There is an increasing trend towards robotic MVR from 2015 to 2023.MiMVR was associated with lower estimated blood loss(EBL)(median 450 vs 1200 mL,P=0.008),major morbidity(14.7%vs 50.0%,P=0.014),post-operative intra-abdominal collections(11.8%vs 50.0%,P=0.006),post-operative ileus(32.4%vs 66.7%,P=0.04)and surgical site infection(11.8%vs 50.0%,P=0.006)compared with oMVR.Length of stay was also shorter for miMVR compared with oMVR(median 10 vs 30 d,P=0.001).Oncological outcomes-R0 resection,recurrence,OS and RFS were comparable between miMVR and oMVR.There was no 30-d mortality.More patients underwent robotic compared with laparoscopic MVR for complex cases(robotic 57.1%vs laparoscopic 7.7%,P=0.004).The operating time was longer for robotic compared with laparoscopic MVR[robotic:602(400-900)min,laparoscopic:Median 455(275-675)min,P<0.001].Incidence of R0 resection was similar(laparoscopic:84.6%vs robotic:76.2%,P=0.555).Overall complication rates,major morbidity rates and 30-d readmission rates were similar between la-paroscopic and robotic MVR.Interestingly,3-year OS(robotic 83.1%vs 58.6%,P=0.008)and RFS(robotic 72.9%vs 34.3%,P=0.002)was superior for robotic compared with laparoscopic MVR.CONCLUSION MiMVR had lower post-operative complications compared to oMVR.Robotic MVR was also safe,with acceptable post-operative complication rates.Prospective studies should be conducted to compare short-term and long-term outcomes between robotic vs laparoscopic MVR.

A Novel Tele-Operated Flexible Robot Targeted for Minimally Invasive Robotic Surgery

In this paper, a novel flexible robot system with a constrained tendon-driven serpentine manipulator(CTSM) is presented. The CTSM gives the robot a larger workspace, more dexterous manipulation, and controllable stiffness compared with the da Vinci surgical robot and traditional flexible robots. The robot is tele-operated using the Novint Falcon haptic device. Two control modes are implemented, direct mapping and incremental mode. In each mode, the robot can be manipulated using either the highest stiffness scheme or the minimal movement scheme. The advantages of the CTSM are shown by simulation and experimental results.

A Robotic System with Robust Remote Center of Motion Constraint for Endometrial Regeneration Surgery

Surgical robots have been widely used in diferent procedures to improve and facilitate the surgery.However,there is no robot designed for endometrial regeneration surgery,which is a new therapy for restoring fertility in women using stem cells.Endometrial regeneration surgery requires processing of the endometrium and transplantation of stem cells with minimal trauma to the uterus.In this paper,we introduce a surgical robotic system that consists of a dexterous hysteroscope,supporting arm,and additional novel instruments to facilitate the operation and decrease trauma to the uterus.Remote center of motion(RCM)constraint is required to protect the cervix of the uterus.First,the supporting arm and hysteroscope are controlled separately in kinematics to ensure that the RCM constraint and hysteroscope’s shape and posture are predictable.Then,a task-decoupled method is used to improve the robustness of the RCM constraint.Experiments confrm that the proposed method is more robust and achieves higher RCM accuracy.In addition,the master-slave control of a robot with RCM constraint is also verifed.This study proposes the realization of a robot with robust RCM control for endometrial regeneration surgery.

Minimally invasive multivisceral resection in rectal cancer:Preparation or Precipitation?

Rectal cancer is a malignant neoplasm that constitutes a significant public health challenge due to its high incidence and associated mortality.In this editorial,we comment on the article by Chan et al.In recent years,there has been progress in the development of new treatments for initial and metastatic rectal cancer due to introduction of techniques of innovative and minimally-invasive surgery(MIS)such as laparoscopy and robotic surgery.However,only a few studies have ana-lyzed the feasibility,safety,and results of MIS in relation to open surgery,thereby highlighting the promising and superior results of MIS in functional and oncolo-gical terms.The findings were corroborated by the comparative study of Chan et al which evaluated the feasibility and safety of minimally invasive multivisceral resection(miMVR).A comparison of postoperative outcomes between open MVR and miMVR showed that miMVR presented less blood loss,fewer postoperative complications,and less morbidity.This editorial article is focused specifically on analysis of the characteristics of new minimally-invasive surgical techniques in rectal cancer,particularly in advanced stages.The importance of future research is emphasized by progress in knowledge,training,and clinical practice in the appli-cation of these surgical procedures for the treatment of advanced colorectal cancer.

Minimally invasive pelvic exenteration for primary or recurrent locally advanced rectal cancer:A glimpse into the future

Surgeons have grappled with the treatment of recurrent and T4b locally advanced rectal cancer(LARC)for many years.Their main objectives are to increase the overall survival and quality of life of the patients and to mitigate postoperative complications.Currently,pelvic exenteration(PE)with or without neoadjuvant treatment is a curative treatment when negative resection margins are achieved.The traditional open approach has been favored by many surgeons.However,the technological advancements in minimally invasive surgery have radically changed the surgical options.Recent studies have demonstrated promising results in postoperative complications and oncological outcomes after robotic or laparoscopic PE.A recent retrospective study entitled“Feasibility and safety of minimally invasive multivisceral resection for T4b rectal cancer:A 9-year review”was published in the World Journal of Gastrointestinal Surgery.As we read this article with great interest,we decided to delve into the latest data regarding the benefits and risks of minimally invasive PE for LARC.Currently,the small number of suitable patients,limited surgeon experience,and steep learning curve are hindering the establishment of minimally invasive PE.

Techniques to resect the distal ureter in robotic/laparoscopic nephroureterectomy

Treatment of clinically-organ confined high grade urothelial carcinoma of the upper tract has historically comprised open nephroureterectomy,with the distal ureter and bladder cuff mobilized through a separate open pelvic incision.To decrease morbidity,urologists have increasingly adopted laparoscopy and robotics in performing nephroureterectomy.In many published series of laparoscopic nephroureterectomy,the distal ureter and bladder cuff are detached from the bladder endoscopically by a variation of the“pluck”technique,with the resulting bladder defect left to heal by prolonged indwelling urethral catheter drainage.While the distal ureter and bladder cuff can be excised laparoscopically,it does require advanced laparoscopic skills.With the wrist articulation and stereoscopic vision in robotic surgery,robotic nephroureterectomy(RNU)and bladder cuff excision can be performed in antegrade fashion to mimic the open technique together with the ability to intracorporeally close the bladder defect in a watertight,mucosa to mucosa fashion after excising the bladder cuff.In this review,we discuss the published minimally invasive techniques in resecting the distal ureter and bladder cuff during laparoscopic and RNU.

Clinical characteristics of remote Zeus robot-assisted laparoscopic cholecystectomy:A report of 40 cases

AIM： To summarize the performing essentials and analyze the characteristics of remote Zeus robot-assisted laparoscopic cholecystectomy. METHODS： Robot-assisted laparoscopic cholecystectomy was performed in 40 patients between May 2004 and July 2005. The operating procedures and a variety of clinical parameters were recorded and analyzed. RESULTS： Forty laparoscopic cholecystectomy procedures were successfully completed with Zeus robotic system. And there were no post-operative complications. Total operating time, system setup time and performing time were 100.3±18.5 min, 27.7±8.8 min and 65.6±18.3 min, respectively. The blood loss and postoperative hospital stay were 30.6±10.2 mL and 2.8±0.8 d, respectively. Camera clearing times and time used for operative field adjustment were 1.1±1.0 min and 2.0±0.8 rain, respectively. The operative error was 7.5%. CONCLUSION： Robot-assisted laparoscopic cholecystectomy following the principles of laparoscopic operation has specific performing essentials. It preserves the benefits of minimally invasive surgery and offers enhanced ability of controlling operation field, precise and stable operative manipulations.