2008.03-2012.06: 美国斯坦福大学，博士
2005.10-2008.03: 美国斯坦福大学，硕士
2000.09-2005.06: 美国莱托诺大学，学士

2022.01-至今...... ：威斯尼斯人网站登录，教授，博导
2019.08-2021.12：威斯尼斯人网站登录，长聘副教授，博导
2016.01-2019.07：威斯尼斯人网站登录，副教授，博导
2013.05-2015.12：威斯尼斯人网站登录，讲师，博导
2012.03-2013.01：美国斯坦福大学生物工程学院，博士后研究员

2018.06-2018.08： 英国帝国理工学院，访问学者
2017.04-2017.08： 美国斯坦福大学机械工程学院，访问学者
2011.05-2011.08： 清华大学精密仪器与机械学系，访问学者

可穿戴传感器和反馈系统、传感器融合算法、人工智能，人体运动训练

2023.01-2024.12，国家自然科学基金外国优秀青年学者研究基金项目，基于日常活动中手势识别的超声软波导研究，负责人
2019.01-2022.12，国家自然科学基金面上项目，基于可穿戴传感网络的全膝关节置换术后的步态训练研究，负责人
2020.01-2021.12，国家自然科学基金外国青年学者研究基金项目，基于手语自动检测的多传感器融合可穿戴手势识别研究，负责人
2016.01-2018.12，国家自然科学基金青年基金项目，基于可穿戴传感和触觉反馈的膝骨关节炎患者步态训练系统研究，负责人
2017.01-2018.12，国家自然科学基金外国青年学者研究基金项目，基于再生能源智能鞋的人体步态训练能量采集研究，负责人
2015.01-2019.12，国家自然科学基金重点项目，深腔作业连续体机器人的运动学分析和力位操控性能综合，参与人
2022.09-2023.06，TensorHealth，肌骨康复可穿戴算法，负责人
2021.08-2022.05，华为技术有限公司，多IMU融合全身姿态检测技术项目，负责人
2020.06-2020.12，博世（中国）投资有限公司，基于BST 传感器和Transfer Learning 的儿童动作识别算法，负责人
2019.09-2020.04，华为技术有限公司，基于手腕肌力的手势识别技术合作项目，负责人
2018.07-2018.12，博世（中国）投资有限公司，基于共享单车的驾驶条件及驾驶者能力智能感知，负责人
2018.11-2022.11，Xsens Technologies，基于评估中风患者的功能评定和运动康复，负责人
2019.05-2019.10，华为技术有限公司，人体步态体态检测技术研究技术合作项目，负责人
2018.04-2021.06，上海市科学技术委员会，下肢助力软体外骨骼工程化样机研制，参与人
2016.01-2018.12，威斯尼斯人网站登录非华裔外籍教师科研激励计划，基于可穿戴传感和触觉反馈的膝骨关节炎患者步态训练系统研究，负责人
2015.07-2020.12，国家青年千人计划，用于人体运动训练和评估的可穿戴式感知和触觉反馈系统，负责人
2014.09-2017.08，威斯尼斯人网站登录-密西根大学联合基金，用于预防老年人跌倒的基于软机器人技术的运动测量反馈系统的研究，负责人
2014.07-2017.06，上海市青年科技英才扬帆计划，用于人体运动训练和评估的可穿戴式感知和触觉反馈系统，负责人
2015.06-2016.12，丹阳市晨辉机电有限公司，基于人体足部运动数据监测与反馈的智能鞋开发项目，负责人
2014.01-2016.06，威斯尼斯人网站登录-绿色普通引进人才科研启动基金，用于人体运动训练和评估的可穿戴式感知和触觉反馈系统，负责人
2015.05-2016.06，北京三星通信技术研究有限公司，基于生物信号的手部动作识别，负责人

期刊论文
1. Li J, Kang P, Tan T, Shull PB, “Transfer learning improves accelerometer-based child activity recognition via subject-independent adult-domain adaption,” IEEE Journal of Biomedical and Health Informatics, In press, 2022.
2. Kang P, Li J, Fan B, Jiang S, Shull PB, “Wrist-worn hand gesture recognition while walking via transfer learning,” IEEE Journal of Biomedical and Health Informatics, In press, 2022.
3. Fan B, Li Q, Tan T, Kang P, Shull PB, “Effects of IMU sensor-to-segment misalignment and orientation error on 3-D joint angle estimation,” IEEE Sensors, 22(3): 2543-2552, 2022.
4. Jiang S, Kang P, Song X, Lo B, Shull PB, “Emerging wearable interfaces and algorithms for hand gesture recognition: A survey,” IEEE Reviews in Biomedical Engineering, 15: 85-102, 2021.
5. Shull PB, Xia H, Charlton JM, Hunt MA, “Wearable real-time haptic biofeedback foot progression angle gait modification to assess short-term retention and cognitive demand,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, 3(29): 1858-1865, 2021.
6. Tan T, Strout ZA, Shull PB, “Accurate impact loading rate estimation during running via a subject-independent convolutional neural network model and optimal IMU placement,” IEEE Journal of Biomedical and Health Informatics, 25(4): 1215-1222, 2021.
7. Chossat JB, Shull PB, “Soft acoustic waveguides for strain, deformation, localization and twist measurements,” IEEE Sensors Journal, 21(1): 222-230, 2021.
8. Wang S, Mo S, Chung RCK, Shull PB, Ribeiro DC, Cheung RTH, “How foot progression angle affects knee adduction moment and angular impulse in people with and without medial knee osteoarthritis: a meta-analysis,” Arthritis Care & Research, 73(12): 1763-1776, 2021.
9. Fan B, Xia H, Xu J, Li Q, Shull PB, “IMU-based knee flexion, abduction and internal rotation estimation during drop landing and cutting tasks,” Journal of Biomechanics, 124: 110549, 2021.
10. Lindsey B, Xu J, Chiasson D, Shull PB, Cortes N, “Feasibility of wearable haptic biofeedback training for reducing the knee adduction moment during overground walking,” Journal of Biomechanical Engineering, 143(4): 044501, 2021.
11. Kang P, Jiang S, Shull PB, Lo B, “Feasibility validation on healthy adults of a novel active vibrational sensing based ankle band for ankle flexion angle estimation,” IEEE Open Journal of Engineering in Medicine and Biology, 2: 314-319, 2021.
12. Li C, Song X, Chen S, Wang C, He J, Zhang Y, Xu S, Yan Z, Jia J, Shull PB, “Long-term effectiveness and adoption of a cellphone augmented reality system on patients with stroke: randomized controlled trial,” JMIR Serious Games, 9(4): e30184, 2021.
13. Xia H, Huang Y, Chen G, Cheng S, Cheung RT, Shull PB, “Self-selected running gait modifications reduce acute impact loading, awkwardness, and effort,” Sports Biomechanics, 1-14, 2021.
14. Tan T, Strout ZA, Xia H, Orban M, Shull PB, “Magnetometer-free, IMU-based foot progression angle estimation for real-life walking conditions,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, 29: 282-289, 2020.
15. Xia H, Charlton JM, Shull PB, Hunt MA, “Portable, automated foot progression angle gait modification via a proof-of-concept haptic feedback-sensorized shoe,” Journal of Biomechanics, 107: 109789, 2020.
16. Xia H, Chen DKY, Zhu X, Shull PB, “Controlled slip energy harvesting while walking,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2(28): 437-443, 2020.
17. Shull PB, Xia H, “Modeling and prediction of wearable energy harvesting sliding shoes for metabolic cost and energy rate outside of the lab,” Sensors, 20(23): 6915, 2020.
18. Chiasson D, Xu J, Shull PB, “Lossless compression of human movement IMU signals,” Sensors, 20(20): 5926, 2020.
19. Jiang S, Gao Q, Liu H, Shull PB, “A novel, co-located EMG-FMG-sensing wearable armband for hand gesture recognition,” Sensors and Actuators A: Physical, 301: 111738, 2020.
20. Gao Q, Jiang S, Shull PB, “Simultaneous hand gesture classification and finger angle estimation via a novel dual-output deep learning model,” Sensors, 20(10): 2972, 2020.
21. Xu J, Cao F, Zhan S, Ling M, Hu H, Shull PB, “Mapping-based dosage of gait modification selection for multi-parameter subject-specific gait retraining,” IEEE Access, 8: 106354-106363, 2020.
22. Jiang S, Li L, Xu H, Xu J, GU GY, Shull PB, “Stretchable e-skin patch for gesture recognition on the back of the hand,” IEEE Transactions on Industrial Electronics, 67(1): 647-657, 2019.
23. Shull PB, Tan T, Culbertson HM, Zhu X, Okamura A, “Resonant frequency skin stretch for wearable haptics,” IEEE Transactions on Haptics, 12(3): 247-256, 2019.
24. Shull PB, Jiang S, Zhu Y, Zhu X, “Hand gesture recognition and finger angle estimation via wrist-worn modified barometric pressure sensing,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, 27(4): 724-732, 2019.
25. Tan T, Chiasson DP, Hu H, Shull PB, “Influence of IMU position and orientation placement errors on ground reaction force estimation,” Journal of Biomechanics, 97: 109416, 2019.
26. Chossat JB, Chen DKY, Park YL, Shull PB, “Soft wearable skin-stretch device for haptic feedback using twisted and coiled polymer actuators,” IEEE Transactions on Haptics, 12(4): 521-532, 2019.
27. Song X, Chen S, Jia J, Shull PB, “Cellphone-based automated Fugl-Meyer assessment to evaluate upper extremity motor function after stroke,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, 27(10): 2186-2195, 2019.
28. Charlton JM, Xia H, Shull PB, Hunt MA, “Validity and reliability of a shoe-embedded sensor module for measuring foot progression angle during over-ground walking,” Journal of Biomechanics, 89: 123-127, 2019.
29. Bao T, Su L, Kinnaird C, Kabeto M, Shull PB, Sienko K, “Vibrotactile display design: Quantifying the importance of age and various factors on reaction times,” PloS one, 14(8): e0219737, 2019.
30. Zhang JH, Chan ZY, Au IP, An WW, Shull PB, Cheung RT, “Transfer learning effects of biofeedback running retraining in untrained conditions,” Medicine and Science in Sports and Exercise, 51(9): 1904-1908, 2019.
31. Maglott J, Chiasson D, Shull PB, “Influence of skill level on predicting the success of one's own basketball free throws,” PloS one, 14(3): e0214074, 2019.
32. Huang Y, Xia H, Chen G, Cheng S, Cheung RTH, Shull PB, “Foot strike pattern, step rate, and trunk posture combined gait modifications to reduce impact loading during running,” Journal of Biomechanics, 86: 102-109, 2019.
33. Jiang S, Lv B, Guo W, Zhang C, Wang H, Sheng X, Shull PB, “Feasibility of wrist-worn, real-time hand and surface gesture recognition via sEMG and IMU sensing,” IEEE Transactions on Industrial Informatics, 14(8): 3376-3385, 2018.
34. Wang J, Xu J, Shull PB, “Vertical jump height estimation algorithm based on take-off and landing identification via foot-worn inertial sensing,” Journal of Biomechanical Engineering, 140(3): 034502, 2018.
35. Uhlrich SD, Silder A, Beaupre GS, Shull PB, Delp SL, “Subject-specific toe-in or toe-out gait modifications reduce the larger knee adduction moment peak more than a non-personalized approach,” Journal of Biomechanics, 66: 103-110, 2018.
36. Li L, Jiang S, Shull PB, Gu GY, “SkinGest: artificial skin for gesture recognition via filmy stretchable strain sensors,” Advanced Robotics, 1-10, 2018.
37. Xu J, Bao T, Lee UH, Kinnaird C, Carender W, Huang Y, Sienko KH, Shull PB, “Configurable, wearable sensing and vibrotactile feedback system for real-time postural balance and gait training: proof-of-concept,” Journal of NeuroEngineering and Rehabilitation, 14(1): 102, 2017.
38. Xia H, Xu J, Wang J, Hunt MA, Shull PB, “Validation of a smart shoe for estimating foot progression angle during walking gait,” Journal of Biomechanics, 61: 193-198, 2017.
39. Shull PB, Zhu X, Cutkosky MR, “Continuous movement tracking performance to predictable and unpredictable tasks with vibrotactile feedback,” IEEE Transactions on Haptics, 10(4): 466-475, 2017.
40. Lin S, Xu J, Zhi X, Chen D, Miao J, Shull PB, Cui D, “Design and fabrication of a stretchable circuit board for wireless posture measurement,” IEEE Electron Device Letters, 38(3): 399-402, 2017.
41. Shull PB, Xu J, Yu B, Zhu XY, “Magneto-gyro wearable sensor algorithm for trunk sway estimation during walking and running gait,” IEEE Sensors Journal, 17(2): 480-486, 2017.
42. Huang Y, Jirattigalachote W, Cutkosky MR, Zhu XY, Shull PB, “Novel foot progression angle algorithm estimation via foot-worn, magneto-inertial sensing,” IEEE Transactions on Biomedical Engineering, 63(11): 2278-2285, 2016.
43. Huang Y, Xu J, Yu B, Shull PB, “Validity of Fitbit, Jawbone UP, Nike+ and other wearable devices for level and stair walking,” Gait & Posture, 48: 36-41, 2016.
44. Zhang D, Xu F, Xu H, Shull PB, Zhu X, “Quantifying different tactile sensations evoked by cutaneous electrical stimulation using electroencephalography features,” International Journal of Neural Systems, 26: 1650006, 2016.
45. Shull PB, Huang Y, Schlotman T, Reinbolt JA, “Muscle force modification strategies are not consistent for gait retraining to reduce the knee adduction moment in individuals with knee osteoarthritis,” Journal of Biomechanics, 48: 3163-3169, 2015.
46. Hernandez F, Shull PB, Camarillo DB, “Evaluation of a laboratory model of human head impact biomechanics,” Journal of Biomechanics, 48: 3469-3477, 2015.
47. Shull PB, Damian DD, “Haptic wearables as sensory replacement, sensory augmentation and trainer–a review,” Journal of Neuroengineering and Rehabilitation, 12(1), 59, 2015.
48. Zhang D, Xu H, Shull PB, Liu J, Zhu X, “Somatotopical feedback versus non-somatotopical feedback for phantom digit sensation on amputees using electrotactile stimulation,” Journal of Neuroengineering and Rehabilitation, 12(1), 44, 2015.
49. Shull PB, Jirattigalachote W, Hunt MA, Cutkosky MR, Delp SL, “Quantified self and human movement: A review on the clinical impact of wearable sensing and feedback for gait analysis and intervention,” Gait & Posture, 40: 11-19, 2014.
50. Sui J, Shull PB, Ji L, “Pilot study of vibration stimulation on neurological rehabilitation,” Bio-medical Materials and Engineering, 24(6): 2593-2601, 2014.
51. Shull PB, Silder A, Shultz R, Besier TF, Delp SL, Cutkosky MR, “Six-week gait retraining program reduces knee adduction moment, reduces pain, and improves function for individuals with medial compartment knee osteoarthritis,” Journal of Orthopaedic Research, 31(7): 1020-1025, 2013.
52. Shull PB, Shultz R, Silder A, Besier TF, Cutkosky MR, Delp SL, “Toe-in gait reduces the first peak in the knee adduction moment during walking in knee osteoarthritis patients,” Journal of Biomechanics, 46: 122-128, 2013.
53. Camarillo DB, Shull PB, Mattson J, Shultz R, Garza D, “An instrumented mouthguard for measuring linear and angular head impact kinematics in American football,” Annals of Biomedical Engineering, 41(9): 1939-1949, 2013.
54. Tenforde AS, Shull PB, Fredericson M, “Neuromuscular prehabilitation to prevent osteoarthritis after a traumatic joint injury,” Physical Medicine and Rehabilitation, 4: S141-144, 2012.
55. Shull PB, Lurie K, Cutkosky MR, Besier TF, “Training multi-parameter gaits to reduce the knee adduction moment with data-driven models and haptic feedback,” Journal of Biomechanics, 44(8): 1605-1609, 2011.
56. Wheeler JW, Shull PB, Besier TF, “Real-time knee adduction moment feedback for gait retraining through visual and tactile displays,” Journal of Biomechanical Engineering, 133(4): 041007, 2011.
57. Bark K, Wheeler JW, Shull PB, Savall J, Cutkosky MR, “Rotational skin stretch feedback: a wearable haptic display for motion,” IEEE Transactions on Haptics, 3(3): 166-176, 2010.
58. Shull PB, Gonzalez RV, “Real-time haptic-teleoperated robotic system for motor control analysis,” Journal of Neuroscience Methods, 151(2): 194-199, 2006.

会议论文
1. Xia H, Kwon J, Pathak P, Ahn J, Shull PB, Park YL, “Design of a multi-functional soft ankle exoskeleton for foot-drop prevention, propulsion assistance, and inversion/eversion stabilization,” IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob), pp. 118-123, 2020.
2. Song X, Ding L, Zhao J, Jia J, Shull PB, “Cellphone augmented reality game-based rehabilitation for improving motor function and mental state after stroke,” IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN), 2019.
3. Maglott J, Shull PB, “Wearable occlusion device for assessing cognitive basketball shooting performance between males and females,” Proceedings of the International Conference on Industrial Control Network and System Engineering Research, pp. 37-41, 2019.
4. Peng D, Strout Z, Jiang S, Shull PB, “A road condition classifier via lock embedded IMU on dock-less shared bikes,” Proceedings of the International Conference on Industrial Control Network and System Engineering Research, pp. 32-36, 2019.
5. Chen DKY, Chossat JB, Shull PB, “HaptiVec: Presenting haptic feedback vectors in handheld controllers using embedded tactile pin arrays,” ACM CHI Conference on Human Factors in Computing Systems, 2019.
6. Shull PB, Xia H, “Energy harvesting modeling and prediction during walking gait for a sliding shoe,” 23rd IEEE International Conference on Digital Signal Processing (DSP), 2018.
7. Zhu Y, Jiang S, Shull PB, “Wrist-worn hand gesture recognition based on barometric pressure sensing,” IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN), pp. 181-184, 2018.
8. Xia H, Shull PB, “Preliminary testing of an angled sliding shoe for potential human energy harvesting applications,” 2nd International Conference on Robotics and Automation Sciences, pp. 147-150, 2018.
9. Xu J, Lee UH, Bao T, Huang Y, Sienko KH, Shull PB, “Wearable sensing and haptic feedback research platform for gait retraining,” IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN), pp. 125-128, 2017.
10. Maglott JC, Xu J, Shull PB, “Differences in arm motion timing characteristics for basketball free throw and jump shooting via a body-worn sensorized sleeve,” IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN), pp. 31-34, 2017.
11. Ling Li, Jiang S, Tao Y, Shull PB, Gu GY, “Fabrication and testing of a filmy “feelingless” stretchable strain sensor,” IEEE/SICE International Symposium on System Integration (SII), pp. 362-367, 2017.
12. Jiang S, Bo Lv, Sheng X, Zhang C, Wang H, Shull PB, “Development of a real-time gesture recognition wristband based on sEMG and IMU sensing,” IEEE International Conference on Robotics and Biomimetics, 2016.
13. Chen DKY, Xu J, Shull PB, Besier TF, “Tactile apparent movement as a modality for lower limb haptic feedback,” International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, pp. 373-383, 2016.
14. Yu B, Bao T, Zhang D, Carender W, Sienko KH, Shull PB, “Determining inertial measurement unit placement for estimating human trunk sway while standing, walking and running,” 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society EMBC, 2015.
15. Huang Y, Guo W, Liu J, He J, Xia H, Sheng X, Wang H, Feng X, Shull PB, “Preliminary testing on a hand gesture recognition wristband based on EMG and inertial sensor fusion,” 8th International Conference on Intelligent Robotics and Applications, 2015.
16. Zhang B, Shull PB, Zhang D, “A simulation study on nerve block by electrical stimulation with high frequency,” 9th International Convention on Rehabilitation Engineering & Assistive Technology, 2015.
17. Shull PB, Jirattigalachote W, Zhu X, “An overview of wearable sensing and wearable feedback for gait retraining,” International Conference on Intelligent Robotics and Applications, pp. 434-443, 2013.
18. Jirattigalachote W, Shull PB, Cutkosky MR, “Virtual pebble: a haptic state display for pedestrians,” IEEE Ro-Man Symposium, pp. 401-406, 2011.
19. Lurie KL, Shull PB, Nesbitt KF, Cutkosky MR, “Informing haptic feedback design for gait retraining,” IEEE World Haptics, pp. 19-24, 2011.
20. Rantala J, Myllymaa K, Raisamo R, Lylykangas J, Surakka V, Shull PB, Cutkosky MR, “Presenting spatial tactile messages with a hand-held device,” IEEE World Haptics, pp. 101-106, 2011.
21. Shull PB, Lurie KL, Shin M, Besier TF, Cutkosky MR, “Haptic gait retraining for knee osteoarthritis treatment,” IEEE Haptics Symposium, pp. 409-416, 2010.
22. Shull PB, Bark K, Cutkosky MR, “Skin nonlinearities and their effect on user perception for rotational skin stretch,” IEEE Haptics Symposium, pp. 77-82, 2010.
23. Lurie KL, Manual J, Shull PB, “Haptic motion training: exploring learning environments for a portable gait retraining system,” IEEE International Symposium on Haptic Audio-Visual Environments and Games, pp. 1-6, 2010.
24. Shull PB, Niemeyer G, “Open-loop bilateral teleoperation for stable force tracking,” IEEE/RSJ International Conference on Intelligent Robots and Systems, pp. 5121-5126, 2009.
25. Shull PB, Niemeyer G,” Force and position scaling limits for stability in force reflecting teleoperation,” ASME Dynamic Systems and Control Conference, pp. 607-614, 2008.
26. Hart JS, Shull PB, Gentry D, Niemeyer G, Roderick S, Akin D, “Wave-variable based force feedback for a space-qualified telerobot,” ASME Dynamic Systems and Control Conference, 303-310, 2008.
27. Shull PB, Niemeyer G, “Experiments in local force feedback for high-inertia, high-friction telerobotic systems,” ASME International Mechanical Engineering Congress and Exposition, pp. 1241-1246, 2007.
28. Awwal AAS, Ferguson WS, Shull PB, “Best angle to orient two intersecting lines," SPIE, pp. 63100-63111, 2006.

设计与制造II(ME209)，可穿戴式系统（ME26012）

1. 副主编: Nature npj Digital Medicine, 2022-至今
2. 副主编: IEEE Journal of Biomedical and Health Informatics, 2021-至今
3. 副主编: IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2017-至今
4. 副主编: Wearable Technologies, 2019-至今
5. 技术委员会委员: IEEE Engineering in Medicine and Biology (EMB) Technical Committee on Wearable Biomedical Sensors and Systems, 2017-至今
6. 技术委员会委员: IEEE International Conference on Wearable and Implantable Body Sensor Networks (BSN), 2019.
7. 技术委员会委员及分会主席: International Conference on Robotics and Automation Sciences, Wuhan, China, June 2018.
8. 编委成员: IEEE Open Journal of Engineering in Medicine and Biology, 2019-
9. 分会主席: International Society of Biomechanics, Brisbane, Australia, July 2017. Session Title: Injury and Rehabilitation.
10. 分会主席 (Irene Davis, co-chair): World Congress of Biomechanics, Boston, MA, USA, July 2014. Session Title: Gait Modification Symposium

2018, 2015 Shanghai Jiao Tong University Mechanical Engineering Department Excellent Researcher Award (Top 10%)
2017，Outstanding Researcher Award, NIH National Center for Simulation in Rehabilitation Research
2017, 威斯尼斯人网站登录烛光奖励计划（优秀教学奖）
2016、2015, 威斯尼斯人网站登录教职工考核中荣获优秀
2014，上海市青年科技英才扬帆计划
2012，在美国NSF （National Science Foundation）国家科学在线期刊发表题为 “Movement Retraining Can Reduce Knee Pain"的综述论文
2011，斯坦福大学 – 清华大学 访问学者奖
2007，美国NSF （National Science Foundation） 本科生研究奖学金