Alois Loidl

822(top 0.1%)

papers

30.0K(top 1%)

citations

83(top 1%)

h-index

138(top 1%)

g-index

844

all documents

30.7K

doc citations

1.3K

citing journals

105

times ranked

1^st most cited paper in Kazan Federal University (2000) [with 169 citations of an article]

1^st most cited author in Kazan Federal University (2005) [with 315 citations of 1 articles]

1^st most cited paper in Kazan Federal University (2005) [with 315 citations of an article]

1^st most cited paper in Azerbaijan National Academy of Sciences (2001) [with 39 citations of an article]

1^st most published author in Johannes Gutenberg University Mainz (1990) [with 10 articles having 905 citations]

1^st most cited author in Johannes Gutenberg University Mainz (1990) [with 905 citations of 10 articles]

1^st most cited paper in Johannes Gutenberg University Mainz (1990) [with 905 citations of an article]

1^st most cited author in Johannes Gutenberg University Mainz (1992) [with 426 citations of 7 articles]

1^st most cited paper in Zentrallaboratorium Deutscher Apotheker (2002) [with 43 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (1998) [with 73 citations of an article]

1^st most cited author in Moscow Power Engineering Institute (1999) [with 128 citations of 3 articles]

1^st most cited paper in Moscow Power Engineering Institute (1999) [with 128 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (2000) [with 382 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (2001) [with 51 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (2004) [with 283 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (2006) [with 602 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (2007) [with 174 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (2008) [with 57 citations of an article]

1^st most cited paper in Moscow Power Engineering Institute (2009) [with 161 citations of an article]

1^st most cited author in University of Burgundy (1989) [with 127 citations of 1 articles]

1^st most cited paper in University of Burgundy (1989) [with 127 citations of an article]

1^st most cited author in Technische Universität Darmstadt (1994) [with 292 citations of 5 articles]

1^st most cited paper in Technische Universität Darmstadt (1994) [with 292 citations of an article]

1^st most published author in Technische Universität Darmstadt (1995) [with 14 articles having 333 citations]

1^st most published author in Technische Universität Darmstadt (1996) [with 9 articles having 419 citations]

1^st most cited author in Aoyama Gakuin University (2015) [with 523 citations of 1 articles]

1^st most cited paper in Aoyama Gakuin University (2015) [with 523 citations of an article]

1^st most published author in University of Augsburg (1998) [with 13 articles having 569 citations]

1^st most published author in University of Augsburg (1999) [with 28 articles having 894 citations]

1^st most cited author in University of Augsburg (1999) [with 894 citations of 28 articles]

1^st most published author in University of Augsburg (2000) [with 30 articles having 1155 citations]

1^st most published author in University of Augsburg (2001) [with 22 articles having 869 citations]

1^st most cited author in University of Augsburg (2001) [with 869 citations of 22 articles]

1^st most published author in University of Augsburg (2002) [with 38 articles having 2340 citations]

1^st most cited author in University of Augsburg (2002) [with 2340 citations of 38 articles]

1^st most cited paper in University of Augsburg (2002) [with 2340 citations of an article]

1^st most published author in University of Augsburg (2003) [with 27 articles having 852 citations]

1^st most published author in University of Augsburg (2004) [with 18 articles having 1347 citations]

1^st most cited author in University of Augsburg (2004) [with 1347 citations of 18 articles]

1^st most published author in University of Augsburg (2005) [with 26 articles having 1997 citations]

1^st most cited author in University of Augsburg (2005) [with 1997 citations of 26 articles]

1^st most cited paper in University of Augsburg (2005) [with 1997 citations of an article]

1^st most published author in University of Augsburg (2006) [with 29 articles having 1434 citations]

1^st most published author in University of Augsburg (2010) [with 21 articles having 653 citations]

1^st most published author in University of Augsburg (2011) [with 26 articles having 1277 citations]

1^st most published author in University of Augsburg (2012) [with 22 articles having 885 citations]

1^st most cited author in University of Augsburg (2012) [with 885 citations of 22 articles]

1^st most published author in University of Augsburg (2013) [with 18 articles having 576 citations]

1^st most published author in University of Augsburg (2014) [with 16 articles having 403 citations]

1^st most published author in University of Augsburg (2015) [with 27 articles having 1365 citations]

1^st most cited author in University of Augsburg (2015) [with 1365 citations of 27 articles]

1^st most cited paper in University of Augsburg (2015) [with 1365 citations of an article]

1^st most published author in University of Augsburg (2016) [with 19 articles having 468 citations]

1^st most published author in University of Augsburg (2017) [with 34 articles having 875 citations]

1^st most cited author in University of Augsburg (2017) [with 875 citations of 34 articles]

1^st most published author in University of Augsburg (2018) [with 19 articles having 467 citations]

1^st most cited author in University of Augsburg (2018) [with 467 citations of 19 articles]

1^st most published author in University of Augsburg (2019) [with 18 articles having 284 citations]

1^st most published author in University of Augsburg (lifetime) [with 545 articles having 22118 citations]

1^st most cited author in Augsburg University (2009) [with 179 citations of 4 articles]

1^st most cited paper in Augsburg University (2009) [with 179 citations of an article]

1^st most cited paper in Budapest University of Technology and Economics (2015) [with 698 citations of an article]

1^st most published author in Academy of Sciences of Moldova (2017) [with 6 articles having 92 citations]

1^st most cited paper in Institut Laue–Langevin (2015) [with 523 citations of an article]

1^st most cited author in Bandung Institute of Technology (2009) [with 178 citations of 1 articles]

1^st most cited paper in Bandung Institute of Technology (2009) [with 178 citations of an article]

1^st most cited paper in University of Mendoza (1996) [with 31 citations of an article]

1^st most cited author in Capital Fund Management (2016) [with 164 citations of 1 articles]

1^st most cited paper in Capital Fund Management (2016) [with 164 citations of an article]

1^st most cited paper in Capital Fund Management (lifetime) [with 164 citations of an article]

1^st most cited paper in Embry–Riddle Aeronautical University (1996) [with 31 citations of an article]

1^st most cited author in State University of Malang (2009) [with 178 citations of 1 articles]

1^st most cited paper in State University of Malang (2009) [with 178 citations of an article]

1^st most cited paper in Paul Verlaine University – Metz (1980) [with 23 citations of an article]

1^st most cited paper in Interstellar Technologies (2015) [with 61 citations of an article]

2^nd most cited paper in Johannes Gutenberg University Mainz (1979) [with 27 citations of an article]

2^nd most cited author in Johannes Gutenberg University Mainz (1982) [with 149 citations of 2 articles]

2^nd most published author in Johannes Gutenberg University Mainz (1988) [with 7 articles having 151 citations]

2^nd most cited author in Johannes Gutenberg University Mainz (1989) [with 309 citations of 5 articles]

2^nd most published author in Johannes Gutenberg University Mainz (1992) [with 7 articles having 426 citations]

2^nd most published author in Moscow Power Engineering Institute (2000) [with 8 articles having 382 citations]

2^nd most cited author in Moscow Power Engineering Institute (2000) [with 382 citations of 8 articles]

2^nd most cited author in Moscow Power Engineering Institute (2004) [with 283 citations of 3 articles]

2^nd most cited author in Moscow Power Engineering Institute (2006) [with 602 citations of 3 articles]

2^nd most cited author in Moscow Power Engineering Institute (2009) [with 161 citations of 3 articles]

2^nd most cited author in Moscow Power Engineering Institute (lifetime) [with 2609 citations of 33 articles]

2^nd most cited author in Technische Universität Darmstadt (1995) [with 333 citations of 14 articles]

2^nd most published author in University of Augsburg (1997) [with 9 articles having 336 citations]

2^nd most cited author in University of Augsburg (2000) [with 1155 citations of 30 articles]

2^nd most published author in University of Augsburg (2007) [with 15 articles having 902 citations]

2^nd most published author in University of Augsburg (2008) [with 18 articles having 646 citations]

2^nd most published author in University of Augsburg (2009) [with 20 articles having 1094 citations]

2^nd most cited author in University of Augsburg (lifetime) [with 22118 citations of 545 articles]

2^nd most cited author in Augsburg University (2006) [with 110 citations of 4 articles]

2^nd most cited author in Capital Fund Management (lifetime) [with 164 citations of 1 articles]

3^rd most cited author in Kazan Federal University (2000) [with 169 citations of 1 articles]

3^rd most cited author in Johannes Gutenberg University Mainz (1986) [with 184 citations of 4 articles]

3^rd most cited paper in Zentrallaboratorium Deutscher Apotheker (lifetime) [with 43 citations of an article]

3^rd most cited author in Moscow Power Engineering Institute (2002) [with 343 citations of 3 articles]

3^rd most cited paper in Moscow Power Engineering Institute (2002) [with 343 citations of an article]

3^rd most cited paper in Moscow Power Engineering Institute (2003) [with 37 citations of an article]

3^rd most cited author in Moscow Power Engineering Institute (2007) [with 174 citations of 1 articles]

3^rd most cited paper in Karlsruhe Institute of Technology (1980) [with 23 citations of an article]

3^rd most cited author in Technische Universität Darmstadt (1996) [with 419 citations of 9 articles]

3^rd most cited paper in Technische Universität Darmstadt (1996) [with 419 citations of an article]

3^rd most cited author in University of Augsburg (1997) [with 336 citations of 9 articles]

3^rd most cited paper in University of Augsburg (1999) [with 894 citations of an article]

3^rd most cited paper in University of Augsburg (2000) [with 1155 citations of an article]

3^rd most cited author in University of Augsburg (2003) [with 852 citations of 27 articles]

3^rd most cited paper in University of Augsburg (2004) [with 1347 citations of an article]

3^rd most cited author in University of Augsburg (2006) [with 1434 citations of 29 articles]

3^rd most cited author in University of Augsburg (2009) [with 1094 citations of 20 articles]

3^rd most cited author in University of Augsburg (2013) [with 576 citations of 18 articles]

3^rd most published author in University of Augsburg (2020) [with 17 articles having 240 citations]

3^rd most cited paper in Saarland University (1985) [with 47 citations of an article]

3^rd most cited paper in Institut Laue–Langevin (1980) [with 28 citations of an article]

3^rd most cited author in Institut Laue–Langevin (2015) [with 523 citations of 1 articles]

3^rd most cited paper in Risø DTU National Laboratory for Sustainable Energy (1985) [with 44 citations of an article]

4^th most cited paper in Johannes Gutenberg University Mainz (1982) [with 149 citations of an article]

4^th most cited author in Johannes Gutenberg University Mainz (1985) [with 103 citations of 1 articles]

4^th most cited paper in Johannes Gutenberg University Mainz (1985) [with 103 citations of an article]

4^th most cited paper in Johannes Gutenberg University Mainz (1992) [with 426 citations of an article]

4^th most cited paper in Technische Universität Darmstadt (1979) [with 27 citations of an article]

4^th most cited paper in Technische Universität Darmstadt (1995) [with 333 citations of an article]

4^th most published author in Technische Universität Darmstadt (1997) [with 7 articles having 104 citations]

4^th most cited author in University of Augsburg (1998) [with 569 citations of 13 articles]

4^th most cited paper in University of Augsburg (2006) [with 1434 citations of an article]

4^th most cited paper in Vilnius University (1997) [with 30 citations of an article]

4^th most cited paper in Augsburg University (2006) [with 110 citations of an article]

4^th most cited author in Budapest University of Technology and Economics (2015) [with 698 citations of 3 articles]

5^th most cited paper in Goethe University Frankfurt (1981) [with 40 citations of an article]

5^th most cited paper in University of Tübingen (1986) [with 63 citations of an article]

5^th most cited paper in Johannes Gutenberg University Mainz (1980) [with 56 citations of an article]

5^th most cited author in Moscow Power Engineering Institute (2005) [with 315 citations of 1 articles]

5^th most cited paper in Moscow Power Engineering Institute (2005) [with 315 citations of an article]

5^th most cited paper in Moscow Power Engineering Institute (lifetime) [with 2609 citations of an article]

5^th most cited paper in Technische Universität Darmstadt (1988) [with 82 citations of an article]

5^th most cited paper in University of Regensburg (1980) [with 28 citations of an article]

5^th most cited paper in University of Augsburg (1998) [with 569 citations of an article]

5^th most cited paper in Federal Research Center "Kazan Scientific Center of the Russian Academy of Sciences" (2007) [with 25 citations of an article]

6^th most cited paper in University of Augsburg (1997) [with 336 citations of an article]

6^th most cited author in University of Augsburg (2011) [with 1277 citations of 26 articles]

6^th most published author in Augsburg University (lifetime) [with 33 articles having 838 citations]

7^th most cited paper in Johannes Gutenberg University Mainz (1986) [with 184 citations of an article]

7^th most cited author in Johannes Gutenberg University Mainz (1988) [with 151 citations of 7 articles]

7^th most cited paper in Johannes Gutenberg University Mainz (1989) [with 309 citations of an article]

7^th most published author in Moscow Power Engineering Institute (lifetime) [with 33 articles having 2609 citations]

7^th most cited paper in University of Augsburg (2001) [with 869 citations of an article]

7^th most cited paper in Augsburg University (2004) [with 59 citations of an article]

7^th most cited paper in Academy of Sciences of Moldova (2003) [with 38 citations of an article]

7^th most cited paper in Academy of Sciences of Moldova (2013) [with 88 citations of an article]

7^th most cited paper in State University of Malang (lifetime) [with 178 citations of an article]

8^th most cited paper in University of Cologne (1986) [with 70 citations of an article]

8^th most cited author in University of Augsburg (2016) [with 468 citations of 19 articles]

8^th most cited paper in Risø DTU National Laboratory for Sustainable Energy (1984) [with 35 citations of an article]

9^th most cited paper in ETH Zürich (1992) [with 226 citations of an article]

9^th most cited author in University of Augsburg (2007) [with 902 citations of 15 articles]

9^th most cited author in University of Augsburg (2014) [with 403 citations of 16 articles]

9^th most cited paper in Institut Laue–Langevin (1993) [with 73 citations of an article]

10^th most cited paper in Johannes Gutenberg University Mainz (1981) [with 77 citations of an article]

10^th most cited paper in Technische Universität Darmstadt (1992) [with 82 citations of an article]

10^th most cited author in University of Augsburg (2008) [with 646 citations of 18 articles]

10^th most cited paper in University of Augsburg (2009) [with 1094 citations of an article]

10^th most published author in University of Augsburg (2021) [with 10 articles having 154 citations]

10^th most cited paper in Augsburg University (2003) [with 37 citations of an article]

10^th most cited author in Augsburg University (2011) [with 130 citations of 3 articles]

10^th most cited paper in Academy of Sciences of Moldova (2006) [with 40 citations of an article]

11^th most cited paper in Kazan Federal University (1995) [with 32 citations of an article]

11^th most cited paper in Technische Universität Wien (2008) [with 105 citations of an article]

12^th most cited paper in Johannes Gutenberg University Mainz (1988) [with 151 citations of an article]

12^th most cited author in Augsburg University (lifetime) [with 838 citations of 33 articles]

12^th most cited paper in Interstellar Technologies (lifetime) [with 61 citations of an article]

13^th most cited author in ETH Zürich (1992) [with 226 citations of 1 articles]

13^th most cited author in Augsburg University (2012) [with 112 citations of 4 articles]

13^th most cited paper in Service de Physique de l'État Condensé (2016) [with 164 citations of an article]

14^th most cited paper in Goethe University Frankfurt (1990) [with 31 citations of an article]

14^th most cited paper in Johannes Gutenberg University Mainz (1991) [with 113 citations of an article]

14^th most cited author in University of Augsburg (2010) [with 653 citations of 21 articles]

14^th most cited paper in University of Insubria (2005) [with 315 citations of an article]

14^th most cited author in Academy of Sciences of Moldova (lifetime) [with 544 citations of 24 articles]

14^th most cited author in Institut Laue–Langevin (1992) [with 141 citations of 4 articles]

15^th most cited paper in Johannes Gutenberg University Mainz (1983) [with 36 citations of an article]

15^th most cited paper in Technische Universität Darmstadt (1990) [with 48 citations of an article]

15^th most cited paper in University of Augsburg (2016) [with 468 citations of an article]

15^th most cited author in University of Augsburg (2019) [with 284 citations of 18 articles]

15^th most cited paper in Institut Laue–Langevin (1987) [with 30 citations of an article]

16^th most cited author in Johannes Gutenberg University Mainz (1991) [with 113 citations of 5 articles]

16^th most cited paper in Augsburg University (2011) [with 130 citations of an article]

16^th most cited paper in Northern Illinois University (2005) [with 128 citations of an article]

16^th most cited paper in Institut Laue–Langevin (1989) [with 54 citations of an article]

17^th most cited paper in Arizona State University (1996) [with 326 citations of an article]

17^th most cited paper in Institut Laue–Langevin (1992) [with 141 citations of an article]

17^th most cited author in Technische Universität Wien (2008) [with 105 citations of 1 articles]

18^th most cited paper in Augsburg University (2012) [with 112 citations of an article]

18^th most published author in Academy of Sciences of Moldova (lifetime) [with 24 articles having 544 citations]

18^th most cited paper in University of Mendoza (lifetime) [with 31 citations of an article]

19^th most cited paper in Kazan Federal University (2002) [with 52 citations of an article]

19^th most cited author in Northern Illinois University (2005) [with 128 citations of 1 articles]

19^th most cited paper in Academy of Sciences of Moldova (2008) [with 54 citations of an article]

20^th most cited author in Russian Academy of Sciences (2002) [with 938 citations of 5 articles]

20^th most cited paper in Russian Academy of Sciences (2002) [with 938 citations of an article]

20^th most cited paper in University of Augsburg (2003) [with 852 citations of an article]

20^th most cited author in University of Insubria (2005) [with 315 citations of 1 articles]

21^st most cited paper in Academy of Sciences of Moldova (2005) [with 40 citations of an article]

21^st most cited paper in Academy of Sciences of Moldova (2010) [with 45 citations of an article]

21^st most cited author in State University of Malang (lifetime) [with 178 citations of 1 articles]

22^nd most cited paper in University of Cologne (1990) [with 73 citations of an article]

22^nd most cited paper in University of Augsburg (2011) [with 1277 citations of an article]

22^nd most cited author in Budapest University of Technology and Economics (2017) [with 207 citations of 6 articles]

22^nd most cited paper in Institut Laue–Langevin (1990) [with 57 citations of an article]

22^nd most cited paper in European Magnetic Field Laboratory (2020) [with 50 citations of an article]

22^nd most cited author in Service de Physique de l'État Condensé (2016) [with 164 citations of 1 articles]

23^rd most cited paper in University of Cologne (1983) [with 34 citations of an article]

23^rd most cited paper in University of Augsburg (2018) [with 467 citations of an article]

23^rd most cited author in Augsburg University (2010) [with 145 citations of 5 articles]

25^th most cited paper in University of Augsburg (2017) [with 875 citations of an article]

25^th most cited author in Arizona State University (1996) [with 326 citations of 1 articles]

25^th most cited paper in Augsburg University (2008) [with 27 citations of an article]

25^th most cited paper in Augsburg University (2010) [with 145 citations of an article]

26^th most cited paper in Langley Research Center (1996) [with 31 citations of an article]

26^th most cited paper in Bavarian Academy of Sciences and Humanities (2013) [with 51 citations of an article]

27^th most cited paper in University of Aveiro (2000) [with 109 citations of an article]

27^th most cited paper in Alternative Energies and Atomic Energy Commission (2005) [with 35 citations of an article]

28^th most cited paper in Osnabrück University (1997) [with 77 citations of an article]

28^th most cited author in Institut Laue–Langevin (2017) [with 105 citations of 2 articles]

30^th most cited author in Russian Academy of Sciences (2006) [with 590 citations of 2 articles]

32^nd most cited paper in University of Cologne (1993) [with 73 citations of an article]

32^nd most cited paper in Technische Universität Darmstadt (1997) [with 104 citations of an article]

32^nd most cited paper in University of Augsburg (2007) [with 902 citations of an article]

33^rd most cited author in Technische Universität Darmstadt (1997) [with 104 citations of 7 articles]

33^rd most cited paper in Türkiye Acil Tıp Derneği (2011) [with 74 citations of an article]

34^th most cited paper in Kazan Federal University (2003) [with 95 citations of an article]

34^th most cited paper in University of California, Berkeley (1986) [with 61 citations of an article]

35^th most published author in Budapest University of Technology and Economics (2017) [with 6 articles having 207 citations]

36^th most cited paper in National Institute of Standards and Technology (1988) [with 41 citations of an article]

37^th most cited paper in Institut Laue–Langevin (lifetime) [with 1278 citations of an article]

37^th most cited paper in European Magnetic Field Laboratory (lifetime) [with 50 citations of an article]

40^th most cited paper in Russian Academy of Sciences (2006) [with 590 citations of an article]

40^th most cited paper in University of Augsburg (2010) [with 653 citations of an article]

40^th most cited author in University of Augsburg (2020) [with 240 citations of 17 articles]

41^st most cited paper in Helmholtz-Zentrum Berlin (2003) [with 25 citations of an article]

43^rd most cited paper in University of Augsburg (lifetime) [with 22118 citations of an article]

43^rd most cited paper in Academy of Sciences of Moldova (2012) [with 23 citations of an article]

43^rd most cited paper in United States Naval Research Laboratory (2001) [with 243 citations of an article]

43^rd most cited author in Institut Laue–Langevin (2011) [with 134 citations of 2 articles]

44^th most cited paper in Academy of Sciences of Moldova (2011) [with 22 citations of an article]

45^th most cited paper in Institut Laue–Langevin (2011) [with 134 citations of an article]

46^th most cited paper in University of Augsburg (2012) [with 885 citations of an article]

49^th most cited paper in University of Augsburg (2008) [with 646 citations of an article]

49^th most cited paper in Institut Laue–Langevin (2017) [with 105 citations of an article]

50^th most cited author in Institut Laue–Langevin (lifetime) [with 1278 citations of 26 articles]

53^rd most cited author in United States Naval Research Laboratory (2001) [with 243 citations of 1 articles]

54^th most cited paper in University of Augsburg (2013) [with 576 citations of an article]

54^th most cited paper in Academy of Sciences of Moldova (2017) [with 92 citations of an article]

55^th most cited author in University of Aveiro (2000) [with 109 citations of 1 articles]

55^th most cited paper in University of Bremen (1996) [with 31 citations of an article]

57^th most cited paper in University of Augsburg (2014) [with 403 citations of an article]

62^nd most cited paper in Helmholtz-Zentrum Dresden-Rossendorf (2017) [with 135 citations of an article]

65^th most cited paper in Academy of Sciences of Moldova (2016) [with 72 citations of an article]

66^th most published author in Institut Laue–Langevin (lifetime) [with 26 articles having 1278 citations]

68^th most cited paper in University of Paderborn (2011) [with 98 citations of an article]

69^th most cited paper in University of Stuttgart (2005) [with 152 citations of an article]

69^th most cited paper in Tohoku University (1990) [with 31 citations of an article]

72^nd most cited author in Russian Academy of Sciences (1999) [with 179 citations of 5 articles]

72^nd most cited paper in Budapest University of Technology and Economics (2017) [with 207 citations of an article]

73^rd most cited paper in ETH Zürich (1993) [with 35 citations of an article]

73^rd most cited paper in Chung-Ang University (2017) [with 172 citations of an article]

73^rd most cited paper in Tata Institute of Fundamental Research (2002) [with 37 citations of an article]

75^th most cited paper in Service de Physique de l'État Condensé (lifetime) [with 181 citations of an article]

77^th most cited paper in Complutense University of Madrid (2001) [with 243 citations of an article]

80^th most cited author in Russian Academy of Sciences (2000) [with 228 citations of 5 articles]

80^th most cited paper in Helmholtz-Zentrum Berlin (2014) [with 36 citations of an article]

81^st most cited paper in Ural Federal University (2019) [with 52 citations of an article]

84^th most cited paper in United States Naval Research Laboratory (1996) [with 31 citations of an article]

90^th most cited author in Helmholtz-Zentrum Dresden-Rossendorf (2017) [with 135 citations of 1 articles]

92^nd most cited paper in National Academy of Sciences of Ukraine (2009) [with 67 citations of an article]

95^th most cited author in Service de Physique de l'État Condensé (lifetime) [with 181 citations of 4 articles]

Rankings

Scientometrics

Citing Bodies

Alois Loidl

Risø DTU National Laboratory for Sustainable Energy