Overcoming Catastrophic Forgetting in Continual Learning by Exploring Eigenvalues of Hessian Matrix.

Neural networks tend to suffer performance deterioration on previous tasks when they are applied to multiple tasks sequentially without access to previous data. The problem is commonly known as catastrophic forgetting, a significant challenge in continual learning (CL). To overcome the catastrophic forgetting, regularization-based CL methods construct a regularization-based term, which can be considered as the approximation loss function of previous tasks, to penalize the update of parameters. However, the rigorous theoretical analysis of regularization-based methods is limited. Therefore, we theoretically analyze the forgetting and the convergence properties of regularization-based methods. The theoretical results demonstrate that the upper bound of the forgetting has a relationship with the maximum eigenvalue of the Hessian matrix. Hence, to decrease the upper bound of the forgetting, we propose eiGenvalues ExplorAtion Regularization-based (GEAR) method, which explores the geometric properties of the approximation loss of prior tasks regarding the maximum eigenvalue. Extensive experimental results demonstrate that our method mitigates catastrophic forgetting and outperforms existing regularization-based methods.

On the philosophical, cognitive and mathematical foundations of symbiotic autonomous systems.

Symbiotic autonomous systems (SAS) are advanced intelligent and cognitive systems that exhibit autonomous collective intelligence enabled by coherent symbiosis of human-machine interactions in hybrid societies. Basic research in the emerging field of SAS has triggered advanced general-AI technologies that either function without human intervention or synergize humans and intelligent machines in coherent cognitive systems. This work presents a theoretical framework of SAS underpinned by the latest advances in intelligence, cognition, computer, and system sciences. SAS are characterized by the composition of autonomous and symbiotic systems that adopt bio-brain-social-inspired and heterogeneously synergized structures and autonomous behaviours. This paper explores the cognitive and mathematical foundations of SAS. The challenges to seamless human-machine interactions in a hybrid environment are addressed. SAS-based collective intelligence is explored in order to augment human capability by autonomous machine intelligence towards the next generation of general AI, cognitive computers, and trustworthy mission-critical intelligent systems. Emerging paradigms and engineering applications of SAS are elaborated via autonomous knowledge learning systems that symbiotically work between humans and cognitive robots. This article is part of the theme issue 'Towards symbiotic autonomous systems'.

[Measurement of personal dose equivalent of X and gamma radiation by ring dosimeter: results of intercomparison measurements]. / Pomiar indywidualnego równowaznika dawki promieniowania X i gamma za pomoca dozymetru pierscionkowego--wyniki porównan miedzylaboratoryjnych.

BACKGROUND: The aim of the study was to present the results of the interlaboratory comparisons for ring dosimeters and to confirm that the applied method is suitable for measuring the personal dose equivalent H(p)(0.07). In addition, calibration procedures used in dosimetric measurements in persons occupationally exposed to ionizing photon radiation X and gamma were presented. MATERIALS AND METHODS: Ring dosimeters made of flexible plastics with the diameter of approximately 20 mm, equipped with two thermoluminescence (TL) detectors type MTS-N, were the subject of interlaboratory comparisons. Irradiated detectors were red out using a new manual TLD's reader (FIMEL, France). All TLD exposures were done for validation of TLD readers and were performed using the reference X-ray and gamma beams with the ISO rod phantom. The methodology of performed exposures corresponded with the methods applied by the European Radiation Dosimetry Group (EURADOS), the European organizer ofinterlaboratory comparisons. RESULTS: The energy, dose and angular characteristics of the ring dosimeter allowed to elaborate the formula for estimating and verifying the personal dose equivalent H(p)(0.07). The test was performed to check and confirm the correctness of the estimated characteristics. The test results were satisfactory, and thus the readiness to implement TLD reader in the used method and to participate in interlaboratory comparisons was confirmed. CONCLUSIONS: According to the requirements of the Polish Centre for Accreditation, the laboratory was participating in the interlaboratory comparison organized by EURADOS in terms of the personal dose equivalent H(p)(0.07). The result of the comparison was satisfactory, therefore the correctness of the testing procedure was confirmed.

Personal dose equivalent Hp(0.07) of medical personnel occupationally exposed to ionizing radiation during 2001-2011.

BACKGROUND: The paper presents the results of the determinations of the personal dose equivalent Hp(0.07) received by medical employees of interventional radiology departments occupationally exposed to X and gamma rays in Poland in 2011, performed by the Nofer Institute of Occupational Medicine in Lódz. The results were compared with the data collected during the last decade. MATERIALS AND METHODS: The dosimetric service provided for medical employees of interventional radiology departments occupationally exposed to ionizing radiation in terms of the personal dose equivalent Hp(0.07). In 2011, personal dosimetry Hp(0.07) determinations performed by the Nofer Institute of Occupational Medicine in Lódz covered 2017 workers employed in 159 medical laboratories. The determinations were performed using ring dosimeters equipped with thermoluminescence detectors according to the procedure accredited by the Polish Centre for Accreditation (document number AB 327). The determinations were carried out in one or two-month periods. RESULTS: Mean annual personal dose equivalent Hp(0.07) in 2011 was equal to 4.9 mSv (annual limit for Hp(0.07) is 500 mSv). The mean annual doses of Hp(0.07) varied from 7.6 mSv in 2001 to 5.6 mSv in 2010. In 2011, two cases of exceeding the annual dose limit of Hp(0.07) were reported. The results show that more than 95% of all examined annual doses did not exceed the level of 10 mSv. CONCLUSIONS: The comparison of the average annual doses and detailed distributions of the doses during the last few years suggests a stabilized level of occupational exposure and an acceptable level of radiological protection in interventional radiology departments monitored by NIOM in Lódz.

[Occupational exposure to X and gamma rays in Poland based on the present and past results (Nofer Institute of Occupational Medicine data]. / Ocena wielkosci dawek efektywnych u osób narazonych zawodowo na promieniowanie rentgenowskie i gamma w Polsce obecnie i w przeszlosci (wedlug danych Instytutu Medycyny Pracy im. Nofera).

BACKGROUND: The paper presents the results of the assessment of effective doses received by people occupationally exposed to X and gamma rays in Poland in 2011 provided by the Nofer Institute of Occupational Medicine in Lodz. The results were compared with the data collected between 1966-2010. MATERIALS AND METHODS: The dosimetric service was provided for people occupationally exposed to ionizing radiation in terms of personal dose equivalent Hp(10). In 2011 the Institute's program of individual dosimetry Hp(10) covered more than 28 000 workers in 4007 laboratories (mainly of health service departments). The measurements were carried out using the film method, according to the research procedure (number AB 327) accredited by the Polish Centre for Accreditation. RESULTS: In 2011 the average annual dose Hp(10) was equal to 0.5 mSv (annual limit for Hp(10) is equal to 20 mSv), which maintained at the approximate level of about 0.5 mSv for the last ten years. At present, more than 99% of annual doses do not exceed 5% of the annual level i.e. the level of 1 mSv. Only one case of exceeding the annual limit was recorded in 2011. CONCLUSIONS: The comparison between the 2011 data on the workers ( mostly health service workers) occupationally exposed to X and gamma rays and the data collected in the previous years indicates a satisfactory level of radiation protection in Poland.

[Occupational exposureto X and gamma rays in Poland in 2010]. / Ocena narazenia zawodowego na promieniowanie rentgenowskie i gamma w Polsce w roku 2010.

BACKGROUND: The paper presents the results of the measurements of ionizing radiation doses received by people occupationally exposed to X and y rays in Poland 2010 provided by the Nofer Institute of Occupational Medicine in Lódz. MATERIALS AND METHODS: The personal dose equivalent Hp(10) measurements were performed using the film method while the Hp(0.07) measurements using ring dosimeters with TL detectors according to the accreditation procedures (No. AB327). The measurements were carried out over two-month periods for Hp(10) and over one- or two-month periods for Hp(0.07). RESULTS: In 2010 the Nofer Institute of Occupational Medicine in Lodz covered more than 27,000 workers with individual whole body dosimetry Hp(10) in 3808 laboratories and 1800 workers with hands dosimetry Hp(0.07) in 152 laboratories. Mean annual dose Hp(10) was 0.5 mSv (annual limit for Hp(10) equals 20 mSv), whereas for Hp(0.07) was 5.6 mSv (annual limit for Hp(0.07) equals 500 mSv). CONCLUSIONS: In 2010, doses higher than the annual limit for both Hp(10) and Hp(0.07) were not recorded. The collected data confirm that the radiation protection of people occupationally exposed to X and gamma rays is satisfactory in Poland.

[Assessment of radiation exposure of miners to radon and its daughter products in selected non-ferrous metal mines]. / Ocena narazenia radiacyjnego górników w wybranych kopalniach metali niezelaznych na radon i produkty jego rozpadu.

BACKGROUND: For over 40 years already, the Nofer Institute of Occupational Medicine (NIOM) in Lodz has been supervising non-ferrous metal mines for miners' radiation risk of radon and its short-lived daughters products found in the air of mines. MATERIAL AND METHOD: The supervision involves the use of trace detectors placed in passive dosemeters worn by a representative group of miners. RESULTS: During the late 1960s, the exposure in some mines was as high as 50 mSv/year. Owing to the steps undertaken in the mines, including primarily the provision of improved ventilation systems, the exposure was reduced to 5 mSv/year, and then to 2 mSv/year during the 1980s and 1990s. CONCLUSION: The results of measurements, performed during the recent 10 years, show that the exposure in non-ferrous metal mines is now within the limits specified for worker category B, i.e., not exceeding 6 mSv/year. The mean annual effective dose for a ten-year (1998-2009) period was 2.1 +/- 0.9 mSv/year.

[Assessment of occupational exposure to photon rays in Poland, 2006]. / Ocena narazenia zawodowego na promieniowanie fotonowe w Polsce w roku 2006.

BACKGROUND: This paper reports the results of the measurement of ionizing radiation doses in people occupationally exposed to gamma or X-ray radiation in Poland, 2006. MATERIALS AND METHODS: The whole-body dose measurements were performed by film dosimeter method, while the hand skin dose measurements were done using thermoluminescence dosimeters, according to AB327 (1) accreditation procedures. RESULTS: In 2006, the whole-body measurements were performed in 3161 people employed in 3635 institutions, while the hand measurements were performed in 805 workers of 62 institutions. Mean Hp(10) dose was 0.49 mSv, whereas mean Hp(0.07) dose was 7.5 mSv. CONCLUSIONS: Having compared the 2006 data with those obtained over the earlier years, it is evident that occupational exposure to X-rays has remained at the same level and the radiological protection in the health care sector is satisfactory.

[Concentrations of natural 226Ra and 222Rn radioisotopes in the water from deep well intakes in the vicinity of Lódz]. / Ocena zawartosci naturalnych izotopów promieniotwórczych radu 226Ra i radonu 222Rn w wodach z ujec glebinowych pochodzacych z okolic Lódzi.

UNLABELLED: BACKGROUND. The towns of Zgierz, Ozorków, Stryków and Glowno are located in the central part of Poland, 10 to 30 km to the north of Lódiz. Large surface water reservoirs are not available in that region, and the inhabitants of this region are supplied with drinking water from deep water sources. Literature data show that water from deep wells may contain various radionuclides, such as radium 226Ra or radon 222Rn, and their activity levels depend, among others, on the age of the geologic formation the water comes from. MATERIAL AND METHODS: An emanation technique employing a low-background system consisting of scintillation chamber with two photomultipliers operating in the coincidence arrangement was used to measure radium and radon concentrations. RESULTS: Radium-226 at levels above the detection level (9 Bq/m3) of the measurement method were not detected in any of the examined deep water sources. Water-solved radon-222 was detected in all tested samples. The measured activities were within the range of 1 kBq/m3 to 13 kBq/m3. CONCLUSIONS: Assuming the maximum concentration value, it is estimated that an annual dose received by the population drinking that water is 0.04 mSv, which is below the value of 0.1 mSv recommended by the World Health Organisation.