Shares in chemicals company Synthomer dropped on Thursday after the company said demand in Europe was weaker than anticipated during March and April, driving the overall group performance lower.Investment group 3i Group failed to impress despite a surge in assets under management (AuM) in the year to March 31st. The group also said that it has identified further cost savings for the future after outperforming its targets last year.Euromoney Institutional Investor, the international online information and events group, was down after it revealed its revenues had declined one per cent in the six months ended March 31st.Thomas Cook was up after it was revealed it had reduced its costs ahead of schedule and gave a favourable outlook for prices and margins.Dixons Retail, the electrical retail, got a lift after it posted a 10% rise in fourth quarter total growth, up four per cent for the full year as a whole.Also higher was Heritage Oil after its revenue soared in the first quarter on the back of an increase in production and on strong performance of interests. FTSE 250 - RisersThomas Cook Group (TCG) 165.10p +14.10%Dixons Retail (DXNS) 39.60p +8.46%Heritage Oil (HOIL) 143.30p +6.86%Inchcape (INCH) 561.50p +6.65%Oxford Instruments (OXIG) 1,608.00p +6.42%Persimmon (PSN) 1,218.00p +6.19%TalkTalk Telecom Group (TALK) 239.60p +5.55%AZ Electronic Materials SA (DI) (AZEM) 322.00p +4.92%Travis Perkins (TPK) 1,549.00p +4.45%Imagination Technologies Group (IMG) 330.60p +4.36%FTSE 250 - FallersSynthomer (SYNT) 207.30p -7.87%3i Group (III) 343.90p -5.37%African Barrick Gold (ABG) 133.20p -4.31%Kazakhmys (KAZ) 337.90p -3.98%Euromoney Institutional Investor (ERM) 992.00p -3.69%Marston's (MARS) 146.80p -3.67%Kentz Corporation Ltd. (KENZ) 386.00p -3.50%Petropavlovsk (POG) 130.80p -3.40%Perform Group (PER) 544.00p -2.86%Hochschild Mining (HOC) 252.00p -2.74%NR